As it happened: #PlutoFlyby

The Nasa briefing has concluded but if you're in the UK and you can't get enough of the #PlutoFlyby, turn on BBC One for the ten o'clock news.

Our science editor David Shukman will be summarising the new findings.

If you've been following our live blog since that dramatic pre-flyby picture arrived, you might remember this...

Well, today a barista has bitten back:

To think that back in 1930, Pluto was a speck of light on Clyde Tombaugh's telescope plates moving against the backdrop of static stars.

Now, that tiny dot has been transformed - for the first time, we can peer in detail onto Pluto's surface.

At the base of the "heart" - now called Tombaugh Regio after Pluto's discoverer - is a young surface, unscarred by craters and dominated by ice mountains more than 3,000m high.

The team here say it doesn't look like anything else in our solar system.

It seems there's nothing quite like Pluto.

A spacecraft flew past Pluto for the first time yesterday.

Today we are discussing the findings.

As some of the chat on social media points out - this science is raw, to say the least!

Chris Lintott is an astrophysicist and co-presents The Sky At Night for the BBC.

Alex Parker is a researcher at the Southwest Research Institute who is involved in image processing for the New Horizons mission.

The mission team are clearly - sorry - over the moon.

Quote Message: I don't think any one of us could have imagined it would be this kind of toy store." from Alan Stern Principal investigator, New Horizons

I don't think any one of us could have imagined it would be this kind of toy store."

Quote Message: This is what we came for." from Will Grundy Co-investigator, New Horizons

This is what we came for."

Quote Message: This exceeds what we came for." from Dr Cathy Olkin Deputy project scientist, New Horizons

This exceeds what we came for."

Every now and again you see something that stops you in your tracks - a stunning sunset or a sight so startling that life seems to pause.

This is one of those moments.

Sitting in an auditorium, on a hot afternoon, with my notebook poised, all around me are the mission's scientists and engineers who can't stop grinning. For many, this must be the proudest episode of their careers.

The detail is phenomenal. Tiny worlds that were specks of light or not even known about have suddenly become reality. We're seeing mountains and abundant frozen water on Pluto, giant canyons on its largest moon Charon, smooth surfaces that indicate active geology and a weirdly-shaped mini-moon, Hydra.

And there's a moving twist too. Naming Pluto's vast pale heart after Clyde Tombaugh who discovered the world in 1930 offers a charming insight into the lineage of astronomy.

You almost have to keep reminding yourself that the new images are not science fiction, but have been brought to us all the way from the edge of the solar system. And this is only the start.

Wow, they didn’t disappoint, did they? And the audience in the theatre here at the Johns Hopkins Applied Physics Lab certainly thought so. Every new picture was introduced with and ooh and an ahh, and then a round of applause.  

Nasa’s science chief John Grunsfeld said earlier this week that there was very little terra incognita left in the Solar System. But in Pluto, Charon and its other moons we are seeing virgin territory. 

Any analysis at this stage still carries a fair bit of speculation because not all of the complementary data is in. But perhaps the biggest news is the suggestion that some of these bodies are still active, that they are not dull objects that died 4.5 billion years ago.  

In the highest resolution image of Pluto, which showed a field of view just 250km across, there were no craters. This is indicative of a young surface, one that may well have experienced recent geological activity. 

NASA-JHUAPL-SwRICopyright: NASA-JHUAPL-SwRI

Now, we’ve seen this kind of thing on moons of giant planets where gravitational tides from the bigger parent can heat up the satellite and deform it. Think of Europa at Jupiter; think of Enceladus at Saturn. But where do you get the heat to drive activity on Pluto? It’s sitting out on its own in the Kuiper Belt with nothing to squeeze it gravitationally. Charon certainly couldn’t do it; it’s too small. 

So, what this tells us is that you do not need ongoing tidal heating to power geology on icy worlds. In science terms that’s certainly a big wow.  

From a blurry distant object to a close up of Pluto's mountains and other features on the frozen surface

Alan Stern, the mission's principal investigator, also said he expects there may be ice volcanoes and geysers on Pluto - he and the team are looking forward to hunting for them in the data still streaming back from New Horizons.

Word is spreading fast about this newly named formation, five billion km from Earth.

That finding of recent activity on Pluto's surface, mission chief Alan Stern says, is "going to send a lot of geophysicists back to the drawing boards".

Spencer adds that Pluto has a "very young surface" - i.e. less than 100 million years old - because of the striking lack of impact craters.

It also has mountains that are at least a staggering 11,000 feet tall.

Spencer now unveils the first view from much closer to Pluto's surface.

It shows what he describes as the dwarf planet's "icy bed-rock" - the team has calculated that these mountainous features must be water ice rather than methane or nitrogen.

NASACopyright: NASA

"This is the first icy world we've visited that hasn't been orbiting a giant planet," Dr Spencer says.

The other worlds like this have all been moons.

John Spencer, a mission co-investigator from the Southwest Research Institute, announces that the heart-shaped region on Pluto is to be named "Tombaugh Regio" - commemorating the discoverer of the dwarf planet, Clyde Tombaugh.

Dr Olkin now explains that Charon has a vast canyon four to six miles deep.

"A small world with much to show us."

Now we see Pluto's giant moon Charon!

NASACopyright: NASA

Quote Message: This image just blew our socks off." from Cathy Olkin Deputy project scientist, New Horizons

This image just blew our socks off."

The first image to be revealed is of the Pluto's littler moon Hydra.

Project scientist Hal Weaver explains that before New Horizons took this picture, we didn't even know how big this moon was.

Now we can just count the pixels!

NASACopyright: NASA

It's about 45km by 30km, and Weaver said it probably contains water ice.

No images yet - but the mission's principal investigator has started with a masterful understatement.

Quote Message: I had a pretty good day yesterday, how about you?" from Prof Alan Stern

I had a pretty good day yesterday, how about you?"

The briefing begins!

Use the Live Coverage tab above to watch.

Our science editor is excited.

The BBC's Rebecca Morelle has taken her pew for the briefing...

Dr Cathy Olkin from the Southwest Research Institute was speaking earlier to our science correspondent Jonathan Amos. 

This is an exciting time for her and the rest of the team. 

Quote Message: This is all so special. We're learning new things every day.

This is all so special. We're learning new things every day.

Quote Message: Every time the spacecraft communicates with the deep-space network and sends its data down - we learn something new. It's just remarkable to me that all this data is sitting on the spacecraft, just waiting for us to unlock its secrets." from Cathy Olkin Deputy project scientist, New Horizons

Every time the spacecraft communicates with the deep-space network and sends its data down - we learn something new. It's just remarkable to me that all this data is sitting on the spacecraft, just waiting for us to unlock its secrets."

Remember you'll be able to watch the briefing right here on this page.

20 minutes to go!

Now the Twittersphere is having fun with that photo of principal investigator Prof Alan Stern...  

New Horizons is an American mission paid for by American taxpayers (thank you). But run through the team members and you’re sure to find some Brits.  

Perhaps the best-known are senior scientists like Fran Bagenal, who grew up in my part of the world (Cambridge), and John Spencer, who’s a Lancashire man. He confesses to still listening to the cricket on the radio even though he’s spent most of his career in the US.  

And then there are the younger scientists like Carly Howett. She hails from Essex and is now affiliated to the Southwest Research Institute, working on New Horizons' Ralph colour camera.  

When I asked her what the past few days have been like, she said: “It’s like England winning the World Cup at the same time as the Ashes, thrown in with Olympic golds and Murray winning Wimbledon.”

Yep, she’s a Brit.

While we all anxiously await the fruits of its labour, New Horizons keeps on moving...

This photo shows New Horizons team members looking over newly downlinked data.

Something seems to have caught Alan Stern's eye! The mission chief is centre right looking rather excited.

NASA/Associated PressCopyright: NASA/Associated Press

One of the pictures we'll get in the next release from the New Horizons team will look very similar to the full-frame image of Pluto that was acquired just before the flyby. Indeed it was taken just 15 minutes prior to the view that so wowed the world. 

The differences between the two will therefore be quite subtle, but they will also be very important. This new image that's coming is the partner image that makes a stereo pair. Stereo is a critical tool to planetary scientists when they're trying to interpret features on the surface. 

 "When you look at an enigmatic surreal terrain, your eye cannot tell which is up and which is down, and the stereo gives you that," explains Will Grundy, a team-member from the Lowell Observatory. 

 "You cannot do shape from shading, because you just have no idea whether the slopes that are tilted towards you are also brighter or are they brighter only because they are illuminated by the sun." 

If you look at Tuesday's stretched-colour image of Pluto, it revealed that the "heart" had two distinct "ventricles", and the division between the two was very pronounced. But what does it signify? Does it indicate different materials, maybe different surface and atmospheric processes at play? 

Before you can start to answer those kinds of questions, you need elevation information. One half of the heart could be a basin, one half could be a plateau - and different things can happen in such diverse settings. 

I don't know if the team will present the pair together, but if they do we'll likely need some of those funny glasses to see the stereo effect. 

Not long now until we hear from the mission scientists again! You'll be able to watch the briefing right here - scheduled to start at 20:00 BST.

Expect to see Pluto and Charon in apparently spine-tingling detail, 10 times better than this (and from a slightly different angle).

NASA/JHUAPL/SWRICopyright: NASA/JHUAPL/SWRI

Speculation is growing about some of the details that images, expected in a few hours from New Horizons, will reveal about the surface of Pluto. 

Co-investigator Will Grundy has been quoted on social media as saying that Pluto is covered in exotic ices - Nitrogen, methane and carbon monoxide - in fact, he says, we've not even made some of these ices in the lab yet! 

No tell-tale signs of liquid on the surface, but he can't rule out sub-surface liquids.

This sounds promising!

Andy Rivkin is a researcher at the Johns Hopkins University Applied Physics Laboratory, home of the New Horizons operations centre. 

Our science editor David Shukman is also at the operations centre in Baltimore, looking forward to the new results. 

The scientists here can't stop smiling this morning.

The data is back. The images are processed. And we've been told that they're spectacular: a full frame shot of Pluto in the best resolution yet, extreme close-ups of its surface - and a snap of its largest moon Charon too, revealed in all its glory.

But... the world will have to wait a little longer to see them! We'll have to hang on until 3pm local time (20:00BST) when they'll be unveiled at mission HQ.

The New Horizons spacecraft is now splitting its time between taking more measurements and sending priority data home.

It will take more than a year to send all of its Pluto payload - not only is the distance vast, but the maximum transmission speed is one kilobit (125 bytes) per second.

NPR science correspondent Geoff Brumfiel makes an earthbound comparison:

Remember you can check when and where signals from New Horizons (code NHPC) are being received on the web page for Nasa's Deep Space Network - currently the goods are coming via Australia...

NASACopyright: NASA

Social media has really taken Pluto to heart - especially the heart shaped region that dominates yesterday's spectacular image. It's been the subject of countless tweets and even members of the New Horizons mission team are getting in on the act.

It didn't all end yesterday! New Horizons is still moving at more than 30,000mph...

This series of images shows how far we came yesterday in our view of Pluto.

Today, the images will get another 10 times better.

The "first look" batch of data, including close-up photos of Pluto and Charon from the flyby, has been spotted by Prof Chris Lintott from the BBC's The Sky At Night.

(He has been watching - closely - the live website for Nasa's Deep Space Network of antennas, which receive the signals after their 5bn km journey...) 

You can expect a lot more from New Horizons over the next day or so - especially at the next main Nasa announcement, expected at 20:00 BST on Wednesday. 

But particularly if you're in the UK (like the online team running this live page) it is probably time for some shut-eye!

Check back tomorrow for more updates - and write down this time:

The name of mission operations manager (MOM) Alice Bowman is now trending on Twitter.

It was also chanted in the auditorium during the briefing - and the journalists in attendance were all on board...

Alan Stern tells the room that the packet of data his team expects to receive on Wednesday morning, US time, has been dubbed "the New York Times data set".

Why?

Quote Message: We think it's going to be pretty interesting." from Prof Alan Stern Principal investigator, New Horizons

We think it's going to be pretty interesting."

Alan Stern, New Horizons mission chief, is speaking now at the briefing (use the Live Coverage tab above).

Half an hour ago he sent this tweet.

Nasa science chief John Grunsfeld emphasises that this is just the beginning - comparing today's flyby event to the landing of the Curiosity rover on Mars.

All the science is still on its way.

Quote Message: If you think it was big today, wait until tomorrow. And the next day." from John Grunsfeld Associate administrator for science at Nasa

If you think it was big today, wait until tomorrow. And the next day."

Sitting among the journalists and other visitors to the operations centre are some special guests...

NASACopyright: NASA

Boy, are there some happy people here in Laurel, Maryland!

I've just spoken with Hal Weaver, the New Horizons project scientist. Like me, he was waiting for the call on the autonomy logs. Unfortunately, neither of us could then hear the next call (because of the cheering), which concerned the status of the solid-state recorder. No matter, it was clear from the faces in the mission operations centre that the recorder was full of data.

"What you heard means the flyby must have worked perfectly," he said.

"All the pictures must be onboard. But obviously I won't quite believe it until I see some of them. We have to make sure that they're not affected by streaking or some other artefacts."

New Horizons dropped the link to Earth at nine minutes past the hour. It's still busy making observations of Pluto and its moons. But it will phone home again during the night, and that will be a much longer pass.

In that contact we'll get a first look at some really high-resolution pictures from the flyby - far more detailed than the spectacular pictures we were shown on Tuesday as a preview to the main event.

Standby for something special from Pluto, its main moon, Charon, and its minor moons Hydra and Nix.

Another briefing is due to start at 02:30 BST.

We will hear a mission status update from the scientists who just flew a probe past Pluto.

Stay tuned...

The crucial call came over what were called the autonomy logs - these recorded any upsets that New Horizons might have had during the flyby. 

The fact that it had none meant the observation sequence must have run without a hitch. 

Controllers will not know until they examine what is in the memory that they did indeed have the data - but all the indications are that this historic fly by was a triumph. 

Well, the cheer this morning for countdown was pretty incredible, but it wasn't a patch on the wave of joy - and relief - that just swept through the auditorium here at mission HQ.

They have heard back: they have a healthy spacecraft with a memory full of images and other science data. Wow.

If you thought the image today was amazing - we haven't seen anything yet...

If you go to the website for Nasa's Deep Space Network you can still see the signal coming through from New Horizons to Madrid.

https://eyes.nasa.gov/dsn/dsn.html

It will drop shortly, Jonathan Amos explains:

Our correspondents at mission control are enjoying the atmosphere.

Quote Message: We have a healthy spacecraft, we have recorded data from the Pluto system, and we are outbound from Pluto.

We have a healthy spacecraft, we have recorded data from the Pluto system, and we are outbound from Pluto.

Quote Message: I can't express how I feel! It's just like we planned it!" from Alice Bowman New Horizons mission operations manager

I can't express how I feel! It's just like we planned it!"

"We are in lock with telemetry from the spacecraft," said mission operations manager Alice Bowman.

And the house came down.

Waiting for a few more details from New Horizons now...

NASACopyright: NASA

Our science editor David Shukman is on the scene...

All we can do is wait...

This is the view a few moments ago in the mission control room.

NASACopyright: NASA

Bustling with excited scientists and engineers!

Remember what it looked like when New Horizons actually soared past Pluto 13 hours ago? 

You can now watch the Nasa briefing - awaiting the "phone home" from New Horizons - using the Live Coverage tab above.

"We are flying through the safest part of the Pluto system," says project scientist Hal Weaver - explaining that New Horizons' path should have been cleared by Pluto's chunky moon Charon.

So the chances are good that we will hear from the probe.

But cross your fingers anyway...

Many people are keen to use today's history-making flyby as an excuse to welcome Pluto back onto the list of our Solar System's nine "official" planets.

This image, and others like it, have had thousands of retweets.

Whether or not Pluto's status is still official - it's inspiring to think that today we've added a significant chunk of knowledge to our understanding of the Solar System.

Read more about the planet-or-not-a-planet controversy here:

http://www.bbc.co.uk/news/science-environment-33462184

While we are waiting for the Nasa briefing to start at 01:30 BST (you'll be able to watch it right here on this page), why not relive the excitement of today's countdown?

This was the moment of New Horizons' closest approach - which it made in radio silence. 

If New Horizons stays silent, these celebrations may have been premature! But all the mission scientists sound very confident that they will get a "phone home" signal in about half an hour's time.

New Horizons' call home is due at 00:53 GMT Wednesday (01:53 BST). It will come through a giant dish in Madrid, Spain - part of Nasa's Deep Space Network of communications antennas.

You can watch it come in yourself at the Nasa Eyes DSN webpage.

NASACopyright: NASA

Receipt of signal should appear on the page no more than about five seconds after the real event.

'The phone will ring'

Now, while we've talked about this tiny concern over New Horizons being damaged in a collision with some icy or dusty debris during its flyby, everyone you speak to on the mission is confident the "phone will ring". But it might not, and if it doesn't there are plenty of benign reasons.

One of the main ones is just the general difficulty of picking up what is a very faint signal. The ground antenna and the probe will go through a series of "handshakes" before a stable link is established. It may take a little while for that process to be completed. Be patient. When it is established and the telemetry starts to come down, controllers will also need a bit of time to understand what it all means.

So, what will they be looking for? They won't be able to see any images or other types of science data. All they'll look for is evidence that the spacecraft is healthy - that in its logs there are no records of any upsets during the period of flyby. And - and this is key - they'll want to see that the memory storage onboard has been filled, because that will suggest all the precious pictures were indeed acquired.

And what if the phone doesn't ring? Or the handshakes are made too late for controllers to get the information they need? Well, we'll all have to come back eight hours later when there is another opportunity for a connection.

Pete Marshall got in touch with another suggested analogy relating to today's historic flyby (see our question three posts ago):

Our science correspondent Jonathan Amos has been speaking to John Grunsfeld, Nasa's head of science.

He was full of excitement and pride, but said the team will be "a little bit concerned" until they hear from New Horizons tonight.

Quote Message: In just 50 years, we've gone from the first flyby of Mars with Mariner 4 to the first flyby of Pluto. 50 years! That's pretty short when you consider that making the first map of the Earth and understanding its continents took hundreds of years.

In just 50 years, we've gone from the first flyby of Mars with Mariner 4 to the first flyby of Pluto. 50 years! That's pretty short when you consider that making the first map of the Earth and understanding its continents took hundreds of years.

Quote Message: In 500 years from now in Encyclopaedia Galactica, if such a thing exists, I think historians will look back at this time and say that it truly was the golden era, or the classical age, of space exploration.

In 500 years from now in Encyclopaedia Galactica, if such a thing exists, I think historians will look back at this time and say that it truly was the golden era, or the classical age, of space exploration.

Quote Message: We still wonder whether New Horizons survived the encounter. We all have our fingers and toes crossed. But every indication is that it should have, and we'll know tonight. It's not exactly the 'seven minutes of terror' (a reference to landing probes on Mars), but we are all a little bit concerned until we actually get the signal from the spacecraft. Lots of things can go wrong.

We still wonder whether New Horizons survived the encounter. We all have our fingers and toes crossed. But every indication is that it should have, and we'll know tonight. It's not exactly the 'seven minutes of terror' (a reference to landing probes on Mars), but we are all a little bit concerned until we actually get the signal from the spacecraft. Lots of things can go wrong.

Quote Message: But as to the question about whether this is going to inspire - I think we've answered that. Just the mission to Pluto was intriguing, and I think we're already inspiring millions and millions of people around the world with the little probe that could." from John Grunsfeld Associate administrator for science at Nasa

But as to the question about whether this is going to inspire - I think we've answered that. Just the mission to Pluto was intriguing, and I think we're already inspiring millions and millions of people around the world with the little probe that could."

When Jonathan sent us these quotes he summed it up as follows:

"We wait for a great day to become a perfect one."

It's gone pretty quiet here at the Johns Hopkins Applied Physics Lab - the mission operations centre for the New Horizons probe.

I can hear a cocktail party in the background as VIP guests while away the time before the expected receipt of the spacecraft's "phone home signal".

Whatever the outcome - and I don't really expect much drama - this has been one of those good days for science, for engineering and just putting it out there.

Principal investigator Alan Stern called it right this morning when we saluted the ingenuity of the human species.

Think about it. It's little more than 110 years since the Wright brothers made the first successful powered flight in an aeroplane, and here we are today with another vehicle - albeit a robot - flying past Pluto at 14km/s at a distance of 4.7 billion km.

The idea that it can go all that way, taking nine and a half years, and arrive at a pre-determined point ready to make the flyby, arriving just 70 seconds early - well, that blows my socks off.

NASA/JHU-APL/SWRICopyright: NASA/JHU-APL/SWRI

Prof Chris Lintott, astrophysicist and presenter of BBC's The Sky at Night, has filed this video round-up of today's events.

"It's been a busy one," he says, demonstrating remarkable powers of understatement.

BBC Two's Newsnight just compared New Horizons' buzzing of Pluto today (a separation of 12,472km at last estimate) to the distance from London to Jakarta. 

That's not bad: 11,715km. 

What's your best analogy? You can tweet Jonathan or Paul with suggestions.

We like saying the craft got within one Earth diameter (about 12,735km on average) - which, apparently, is also about half the total length of the Great Wall of China !

Not bad after travelling five billion km...

Nasa's now world-famous probe has (hopefully) already sent its "phone home" message! That much-anticipated signal should be received at approximately 01:53 BST.

There will be a live broadcast from mission control starting at 01:30 BST.

Meanwhile - this graphic from the official New Horizons Twitter account is a nice reminder of how far away the little spacecraft is, and the vast territory that it is headed into...

In a recorded message to the New Horizons team, Cambridge University astrophysicist Prof Stephen Hawking congratulated them on their "pioneering mission"....

Quote Message: Billions of miles from Earth, this little robotic spacecraft will show us the first glimpse of mysterious Pluto

Billions of miles from Earth, this little robotic spacecraft will show us the first glimpse of mysterious Pluto

He noted that it was 50 years since Mariner 4, the first successful mission to Mars, sent back 21 images of Earth's neighbour. Now New Horizons will uncover new details of a much more distant red planet.

Quote Message: We explore because we are human and we want to know

We explore because we are human and we want to know

You can see the video message in its entirety here:

A lot of messages of affection for Pluto have been shared on social media today, in response to the "heart" it flashed at Earth.

This one has been shared so widely it's hard to know where it started...

TwitterCopyright: Twitter

Meanwhile US astronaut Scott Kelly, who is four months into a year in space, sent this one from the International Space Station!

If you're in the UK, tune into Newsnight now on BBC Two!

Our science correspondent Rebecca Morelle is about to give a live update from Baltimore...

And if you missed Rebecca's short film all about Pluto on Newsnight yesterday, you can find it in the "Key Video" tab above...

Adham Fisher, Leicester:

Email Message: I don't think this mission can be called a "visit" to Pluto, as some have termed it. The craft has not landed on the planet or even broken its atmosphere. The Mars Rover mission, however, has definitely been a "visit". 

This "fly-by" is just that, or a sightseeing tour, but an extremely ground breaking one nevertheless, which will show things we have never seen before.

How splendid and fitting that the ashes of Pluto's discoverer were sent with New Horizons. I don't know if that has been done before, but might he now be the furthest human away from Earth?

I don't think this mission can be called a "visit" to Pluto, as some have termed it. The craft has not landed on the planet or even broken its atmosphere. The Mars Rover mission, however, has definitely been a "visit". 

This "fly-by" is just that, or a sightseeing tour, but an extremely ground breaking one nevertheless, which will show things we have never seen before.

How splendid and fitting that the ashes of Pluto's discoverer were sent with New Horizons. I don't know if that has been done before, but might he now be the furthest human away from Earth?

As far as we know, Adham, yes - that portion of Tombaugh's ashes are the farthest-flung human remains, by quite some distance!

While we're waiting for New Horizons to spin around and ping a message home - look at Pluto itself spinning! 

Amateur space imager  Björn Jónsson created this animation showing Pluto rotating in all its new high-resolution glory.

It is built up from images taken during New Horizons' approach, right up to - and including - the full-frame shot snapped just before the flyby and released today.

There's something refreshingly raw about covering this extraordinary and uplifting story. As we catch the scientists in the corridors or listen in to their briefings, one impression is overwhelming: that they're blissfully ignorant about what's hitting them and are rather enjoying the novelty of not being able to explain anything.

This is because the Pluto venture is discovery in its purest, least processed and most thrilling form. We're experiencing the cosmic equivalent of landing on a totally unexplored shore. I keep picturing someone like Charles Darwin startled by a strange animal and having no frame of reference to even begin to understand it. Pluto and its moons are so unknown that every hour seems to bring more surprises. And, when we ask questions, we no longer expect confident answers but have become used to hearing an amused "don't know".

Other favourite phrases include "well, that's just an idea" and "this is our first attempt on the back of an envelope". One that may become classic was the scientist who started to offer an explanation before admitting with a chuckle that he was only thinking of a theory and that "he was making it up right now". Everyone laughed with him. And this makes the mission all the more exciting. Usually us journalists are dealing with finished, polished research findings. Not here. We all feel like we're on the journey of discovery too.

Very soon, New Horizons will start to transmit a signal to Earth to tell the mission team it has achieved its objectives. That's a slight exaggeration: it's a report on the health status of the probe, but this will be enough for controllers to know the flyby was very likely successful.

But the thing you should try to grasp is the vast distance this radio message must cover. Today, New Horizons is 4.7 billion km from Earth. At this separation, a light signal takes a shade over four hours and 25 minutes from transmission to receipt. Therefore, if the probe sticks to the plan and starts to send its telemetry at 20:27 GMT, it should be hitting Nasa's antenna at 00:53 GMT, Wednesday (01:53 BST).

But the eye-opener is how long the signal takes just to cross the orbits of the outer planets on its way into the inner Solar System. It takes almost half an hour to cross the orbit of Neptune, and it's almost two hours before it crosses the orbit of Uranus. And by the time it gets to Saturn, it's been in flight for just over two hours and fifty minutes. The Solar System really is a big place, and Pluto really is a long, long way from Earth.

New Horizons is now soaring away from Pluto but it is still working to collect information.

It hasn't even paused yet to send its "phone home" message to say all is well!

So, now we’ve got some proper colour images of Pluto and its main moon, Charon, taken on Monday and returned prior to the flyby. 

They come from New Horizons’ Ralph camera. It’s the information from this camera that was used to colour the spectacular black-and-white image of Pluto released earlier on Tuesday, taken with the long-range camera, Lorri. The advantage of Lorri is that it has four times the resolution of Ralph, but Ralph has some special tricks up its sleeve that Lorri doesn’t.  

NASA/JHUAPL/SWRICopyright: NASA/JHUAPL/SWRI

One of the things you can do with its pictures is stretch the colours to amplify property differences in surface materials. You wouldn’t ordinarily see such differences in just a black-and-white image. When you do this stretching with Pluto, you see its “heart” is actually two very distinct regions. Two distinct ventricles, if you like. The north pole of Pluto looks very yellow in this treatment, and we also see linear features starting to emerge. 

All of this can hint at differences in composition and surface processes.  

“From the ground, we knew there were a lot of colours on Pluto, but we never imagined anything like this,” said Cathy Olkin, the New Horizons deputy project scientist. 

But remember, these colours are exaggerated.  

The same approach to Charon highlights its unusual dark pole. Quite why it is so dark is a mystery, but the Ralph data is opening ideas. One is that atmospheric molecules are coming off Pluto and hitting Charon. They bounce around and stick to where it’s coldest – the poles. Once stuck, they get processed by ultraviolet light and cosmic rays to produce more complex – and darker – molecules referred to as tholins. 

This is science on the go!  

It's only lunchtime here, but some of the scientists are starting to look a little bleary eyed.

I just chatted to John Spencer - part of the New Horizons science team - who said he'd had about an hour's sleep last night.

He was up until 3am processing the Pluto image that has so wowed the world today. It involves combining information from the probe's black and white hi-res camera with what was captured by the lower-res colour imager, Ralph. But - and I think everyone would agree - it was worth losing a bit of sleep over!

Later we might see some more colour images coming back - with patches of deep orange and black standing out against the soft beige backdrop.

Alan Puckey:

Email Message: Let's hope mankind never loses the ambition to explore our place in the wider universe we exist in. If only we could achieve this amount of collaboration across our little world - for the peace of all our people.

Let's hope mankind never loses the ambition to explore our place in the wider universe we exist in. If only we could achieve this amount of collaboration across our little world - for the peace of all our people.

Timothy Smith:

Email Message: Come 11:00p EST, I'll have on my NASA shirt, have popcorn and beer ready, and have my TV tuned to NASA TV. Let's do this!

Come 11:00p EST, I'll have on my NASA shirt, have popcorn and beer ready, and have my TV tuned to NASA TV. Let's do this!

As they endure the long wait before receiving confirmation from New Horizons that it has safely flown past Pluto, scientists at mission headquarters have been outlining some of the features that might become apparent on the dwarf planet when the probe begins to download images tomorrow evening. There have been discussions about the red colour, tectonic plates, even mountains!

The bright white area at the bottom of the most recent image, rapidly dubbed the "heart" has provoked much comment on social media. 

Others have been using the flyby as an opportunity to re-open old wounds about Pluto's status - planet or dwarf planet?

And some have used the long gap between flyby and "phone home" to polish their artistic skills....

Richard Bevan:

Email Message: A wonderful achievement – 4 billion kilometres, 9 ½ years and 72 seconds early.  If only the trains on my morning commute were that reliable!!

A wonderful achievement – 4 billion kilometres, 9 ½ years and 72 seconds early.  If only the trains on my morning commute were that reliable!!

Tom Spencer:

Email Message: Truly an epic moment in the history of discovery for mankind. It seems limitless what we can achieve when we put our minds to the task! Hooray for NASA!

Truly an epic moment in the history of discovery for mankind. It seems limitless what we can achieve when we put our minds to the task! Hooray for NASA!

Siobhán, Norwich:

Email Message: I find it a bit surreal knowing that something sent into space when I was 19 is now doing what it was built to do. However as a teacher, seeing the look of bewilderment on my children's faces as they comprehend the fact that the photo of Pluto has come about from a journey that began when they were two is amazing. Being able to share this with them through the live conference, the live updates, Newsround and BBC News is what science is all about - bringing awe and wonder to all!

Can't wait for more pictures to arrive. 

I find it a bit surreal knowing that something sent into space when I was 19 is now doing what it was built to do. However as a teacher, seeing the look of bewilderment on my children's faces as they comprehend the fact that the photo of Pluto has come about from a journey that began when they were two is amazing. Being able to share this with them through the live conference, the live updates, Newsround and BBC News is what science is all about - bringing awe and wonder to all!

Can't wait for more pictures to arrive. 

Here’s looking at you, kid! The Rosetta probe has taken a picture of Pluto.  Okay, Europe’s spacecraft, which orbits Comet 67P, is a long, long way away from the dwarf planet, but the dot-like picture is still neat. Why? Because both objects – Comet 67P and Pluto – are Kuiper Belt objects.  

The comet likely originates from that same zone of the Solar System where the dwarf planet continues to live. Somehow, the icy dirt-ball got disturbed and sent into the inner Solar System. In fact, we think there are quite a few KB objects that have done this, and not just comets.  

Triton, the moon of Neptune, is very probably a one-time Kuiper Belt resident that got thrown inwards, only to be captured in the gravity of the gas giant. Today, Rosetta and Comet 67P are 194 million km from the Sun. New Horizons and Pluto, on the other hand, are 4.9 billion km from the Sun. Both are great space missions. If 2014 was the “year of the comet”, then 2015 is very definitely the “year of Pluto”.

ESA/Rosetta/MPS for OSIRIS TeamCopyright: ESA/Rosetta/MPS for OSIRIS Team

After the elation and cheers at the moment of closest approach and the gasps after the incredible picture was revealed - things are now starting to get a tiny bit tense.

The scientists here won't find out for many hours whether this flyby has actually worked or not.

At a press briefing, Alan Stern said there's a chance of about one in 10,000 that New Horizons could fail. But he said he's confident that won't happen.

After nearly a decade of waiting, I reckon these last few hours will feel like an eternity for the New Horizons team...

JHUAPLCopyright: JHUAPL

Quote Message: I am feeling a little bit nervous like you do when you set your child off, but I have absolute confidence that it is going to do what it needs to do to collect that science, and it's going to turn around and send us that burst of data and tell us that it's ok. I'm nervous and proud at the same time. from New Horizons mission operations manager Alice Bowman

I am feeling a little bit nervous like you do when you set your child off, but I have absolute confidence that it is going to do what it needs to do to collect that science, and it's going to turn around and send us that burst of data and tell us that it's ok. I'm nervous and proud at the same time.

Caol, Glasgow:

Email Message: "I have been watching the developments of New Horizon with excitement. I had totally forgot that this probe was making the journey until last year. The excitement seems to be dumbfounding some of my friends and colleagues who fail to see see the significance.

As for Big Cat's 'Pluto Putdown'.... what did he expect. I imagined a cold grey featureless rock due to its distant orbit only to be greeted with what are spectacular and vivid images of a world that might as well be considered an exo-planet with its own detailed history.

Far from being underwhelmed, I am elated and excited at the character of this dwarf planet."

"I have been watching the developments of New Horizon with excitement. I had totally forgot that this probe was making the journey until last year. The excitement seems to be dumbfounding some of my friends and colleagues who fail to see see the significance.

As for Big Cat's 'Pluto Putdown'.... what did he expect. I imagined a cold grey featureless rock due to its distant orbit only to be greeted with what are spectacular and vivid images of a world that might as well be considered an exo-planet with its own detailed history.

Far from being underwhelmed, I am elated and excited at the character of this dwarf planet."

Paramjit Grewal:

Email Message: It is a tribute to science, to reach so close and see minute detail at such distances.

It is a tribute to science, to reach so close and see minute detail at such distances.

In some ways, this will be one of the most memorable pictures this week. It shows New Horizons team members at the moment they first saw the full-frame image of Pluto released today.

The team saw it hours before the rest of the world, at their morning briefing. What you see is unbridled joy after nine-and-a-half years of flight across the Solar System, and many more years of development before that.

New Horizons probably has its origins in scientific meetings held in the late 1980s. If you'd worked all that time just for this moment, you'd jump out of your seat as well.

NASACopyright: NASA

In response to our earlier post about New Horizons radio signals being received in Australia,  Frank Desmond emails:

Email Message: Please tell me that that tracking station is, literally, The Dish as seen in the movie from the year 2000 about Apollo 11 landing on the moon.

(The part I still remember is the school orchestra asked to play the American National Anthem and so start playing...... the Hawaii 5-0 theme.)

Please tell me that that tracking station is, literally, The Dish as seen in the movie from the year 2000 about Apollo 11 landing on the moon.

(The part I still remember is the school orchestra asked to play the American National Anthem and so start playing...... the Hawaii 5-0 theme.)

Actually Frank, that dish was in Parkes in New South Wales. The tracking station receiving New Horizons data is just outside Canberra.

Coincidentally, it would take about as long to drive between the two as it does for NH radio signals to transmit home from Pluto!

The historic flyby of the dwarf planet plainly isn't everyone's cup of tea - or coffee....

The world’s media descend on to the stage after the press briefing to talk to Alan Stern, New Horizons’ principal investigator. 

I reach out to grab his hand to offer congratulations.  He hangs on to it, and we discuss the significance of the day. 

“Aren’t we an amazing species, a truly amazing species?” he says.

Mission chief Alan Stern says there is evidence of "surface activity" on Pluto, a tantalising hint of earth-like tectonics "in its past or even its present".

But might it snow?

Quote Message: “It is clearly a world where both geology and atmosphere, climatology, play a role. Pluto has strong atmospheric cycles, it snows on the surface, the snows sublimate and go back into the atmosphere each 248 year orbit…” from Alan Stern, New Horizons principal investigator

“It is clearly a world where both geology and atmosphere, climatology, play a role. Pluto has strong atmospheric cycles, it snows on the surface, the snows sublimate and go back into the atmosphere each 248 year orbit…”

You have to take your hat off to the space navigators. The ability today to drive probes precisely around the Solar System is extraordinary.

To get into position for today's flyby, New Horizons had to hit a "keyhole" in space just 100km by 150km, and arrive at that location within a set margin of 100 seconds.

The last indications were that New Horizons was on the button of that aim point, being perhaps 70km closer to the surface of Pluto than anticipated, and arriving about 72 seconds early. But, hey, that's pretty good going after a multi-billion-km flight lasting nine and a half years.

It does mean of course that with a closest approach of 12,472km from the surface (rather than 12,542km as planned), the best images will have just a little bit better resolution than expected.

We can live with that.

A reminder, as mentioned earlier, that there is a very small chance New Horizons will come a cropper. 

The team, led by principal investigator Prof Alan Stern, sounds confident!

Nasa has released some images showing tension and jubilation among members of the New Horizons team, waiting to see the fresh image of Pluto.

EPA/NASACopyright: EPA/NASA

EPA/NASACopyright: EPA/NASA

The cheering and jubilation are phenomenal. There's a powerful sense of achievement at sending a robotic craft three billion miles to Pluto.

But there's also something much more instinctive: the thrill of witnessing and sharing a great moment of discovery. Most moving for me has been catching a few words with the son of the man who first found Pluto.

Al Tombaugh is obviously delighted that a sample of his father Clyde's ashes is on board New Horizons, speeding past Pluto and now heading into the unexplored realm of the Kuiper Belt. I asked Al if his father would have wanted to visit the tiny world. Maybe, he said, but he was always worried about the physical strain of life as an astronaut.

BBCCopyright: BBC

Another thought that's very striking here today: so many scientists and engineers and technicians have had a hand in making this mission work, and their excitement is totally justified.

So what about the coming hours? No one here will truly relax until the next signals reach home as the spacecraft slips beyond Pluto.

As word of its flyby, and the last image it took beforehand, travel around the world - it's worth remembering that New Horizons is still frantically acquiring photos and measurements.

Shortly after passing Pluto, it made its closest approach to the dwarf planet's biggest moon, Charon, at 13:04 BST.

NASACopyright: NASA

We'll hear from it again - with any luck - in just over 12 hours' time.  

The briefing is underway - click the "Live Coverage" tab above to watch.

It's a very, very big day for the New Horizons team.

Quote Message: This is true exploration...that view is just the first of many rewards the team will get. Pluto is an extraordinarily complex and interesting world. from Alan Grunsfeld, Nasa associate administrator

This is true exploration...that view is just the first of many rewards the team will get. Pluto is an extraordinarily complex and interesting world.

NasaCopyright: Nasa

Wow. 15 minutes out from New Horizons' closest approach - this is what the mission control room looked like!

As you've heard from our science correspondent Jonathan Amos - the probe is too busy to phone home until much later tonight.

You'll get all the updates right here!

A tweet from our science editor David Shukman, also at the operations centre in Maryland:

Coming up at 13:15 BST there will be a briefing direct from the New Horizons operations centre - including an update on what the team received from the probe last night, before it went silent for the flyby.

You can watch using the "Live Coverage" tab above.

Quote Message: “We have completed the initial reconnaissance of the Solar System, an endeavour started under President Kennedy more than 50 years ago and continuing to today under President Obama. It’s really historic what the US has done, and the New Horizons team is really proud to have been able to run that anchor leg and make this accomplishment.” from Alan Stern, New Horizons principal investigator

“We have completed the initial reconnaissance of the Solar System, an endeavour started under President Kennedy more than 50 years ago and continuing to today under President Obama. It’s really historic what the US has done, and the New Horizons team is really proud to have been able to run that anchor leg and make this accomplishment.”

A "love note" from 4.7bn km, they're calling it. Do you like it?

This is the last full-frame image that New Horizons sent down to Earth before going radio silent for the flyby. What you see is a combination of data - of a high-resolution, black-and-white image from the probe's Lorri camera, and colour information from the spacecraft's lower-resolution Ralph camera.

In this view, Lorri sees the surface at about 4km per pixel, while Ralph's information is roughly 28km per pixel. So, it's a bit of clever work on the part of the image processors.

NASA/JHUAPL/SWRICopyright: NASA/JHUAPL/SWRI

The lighter areas, like the "heart", are probably the younger terrains, containing perhaps methane and carbon monoxide frosts.

The dark regions are probably older, and contain materials that have been through the mill in terms of exposure to UV light and cosmic rays. We might be seeing more complex hydrocarbons in these regions.

This image is an insurance policy: if we never hear from New Horizons again, we will have had, at the very least, this spectacular vista. And I'm fairly sure this might actually be the picture that goes in all future coffee table books about space.

Simon Briggs:

Email Message: This and the Philae robotic European Space Agency lander that accompanied the Rosetta spacecraft which landed on comet 67P/Churyumov–Gerasimenko are two of the most exciting solar system projects for ages.

As a follow-up to the email sent by Bruce Boatman, I am in total agreement with this, though in future any projects on a grander scale will require further international cooperation. One success story has been the International Space Station, but similarly more is needed.

This and the Philae robotic European Space Agency lander that accompanied the Rosetta spacecraft which landed on comet 67P/Churyumov–Gerasimenko are two of the most exciting solar system projects for ages.

As a follow-up to the email sent by Bruce Boatman, I am in total agreement with this, though in future any projects on a grander scale will require further international cooperation. One success story has been the International Space Station, but similarly more is needed.

Congratulations New Horizons!

Although we can't know for sure until later tonight when it "phones home" - according to its trajectory and its programme of movements, a spacecraft just made the first ever flyby of Pluto.

It shot past just 12,500km away - that's the diameter of Earth, or half the length of the Great Wall of China.

NASA/JHUAPL/SWRICopyright: NASA/JHUAPL/SWRI

New Horizons hasn't got far to go!

Its closest approach will be at 12:49:57 BST - start your countdowns....

A great deal of enthusiastic speculation is underway about what this breathtaking new image can tell us about Pluto.

BBC Sky At Night presenter Prof Chris Lintott and space journalist Emily Lakdawalla lead the way...

Wow - look at this image - it seems to have snuck out early.

We'd been promised it would be awesome, but Pluto turns out to be truly stunning.

NASA/JHUAPL/SWRICopyright: NASA/JHUAPL/SWRI

A tiny world with a huge heart!

Nasa's New Horizons Instagram account appears to have shared that highly anticipated picture!

This, then, was Pluto as the probe prepared to barrel past and take its close-up measurements.

Wow!

I've just bumped into Seti's Mark Showalter who discovered some of Pluto's moons. He said he's seen the final image sent down before Pluto went 'radio silent' for the flyby - he told me that it's amazing and that we won't be disappointed.

Expect to see the Pluto image not long after the flyby - and the tomorrow we get the real close ups.

It won't be released until (hopefully) the Nasa briefing at 13:00 BST - but there is tantalising gossip about the last photo New Horizons snapped before the flyby...

New Horizons will only get within 12,500km of Pluto - so it would have to be a good shot to plant a flag.

But US patriotism is alive and well at the operations centre:

Don't get hung up on it, but there is a very small chance that New Horizons won't succeed today.

As it flies through the Pluto system, it could encounter small pieces of icy debris, and if it hits one of these full square in the face, it could do a lot of damage. Something pebble-sized would be lethal if it wanders into the path of a spacecraft moving at 50,000km/h.

On approach to Pluto, the mission team looked for possible obstacles and could find none of any significance. The probability of running into something is, they say, a one-in-10,000 risk.

Even if an icy stone "flicks up at the windscreen", engineers have confidence that New Horizons will cope. It's got Kevlar and other protective materials covering its key components.

It also carries a lot of redundancy, meaning if one system goes down, another is ready to take over.

What will you get done in the next hour?

New Horizons will travel a distance 1.2 times longer than the Earth's equator - taking historic pictures and measurements all the way...

One of the many weird and wonderful things about Pluto is the chaotic behaviour of the dwarf planet's moons. 

About one hour ago, New Horizons took its best colour image of the rugby ball-shaped moon Nix.

We won't see that pic for days, weeks or months, depending on its position in the queue of data to be sent back to Earth.

But you can see Nix's peculiar motion in this computer simulation, which compresses four years into two minutes. 

The tumbling is caused by the strange nature of Pluto and Charon, which are effectively a double planet and share a common centre of gravity located in the space between them. The variable gravitational fields cause the smaller moons to spin erratically.    

Scientists and media carb loading before the countdown

Here's the strange thing today: It's all quiet. Literally. New Horizons is busy getting on with its business some 4.7 bn km from Earth, and we're all in the dark.

That's because the probe is not talking to Earth while it's observing Pluto and its moons. So, why is that? Why did New Horizons drop its link to Earth today, of all days?

Well, it's down to the configuration of the spacecraft. It doesn't carry a moveable antenna. To speak to Earth, it actually has to turn its whole body around and point in a certain direction. And, obviously, it can't do that if, at the same time, it's trying to point its cameras and other instruments at the dwarf planet and its satellites.

New Horizons will make hundreds of manoeuvres today during its observation sequence, swivelling itself every which way with the help of little thrusters. Only when the "goods are in the bag" will it turn again to talk to us.

David Shaw , a proud Chelmsford resident, has been in touch to remind us that some UK tech is on board New Horizons:

Email Message: The camera used on the spacecraft was produced at e2v in Chelmsford, Essex.

The camera used on the spacecraft was produced at e2v in Chelmsford, Essex.

In fact,  e2v  also provided some of the sensors on Rosetta, the European Space Agency probe that sent us historic pictures of comet 67P last November (and continues to work as the comet approaches the Sun).

As the little probe hurtles closer and closer...

...it has been receiving (and retweeting) some celebrity endorsements!

That's right - New Horizons launched in January 2006. 

It was 15 months earlier, in October 2004, that Donny had his most recent UK top 10 single, Breeze On By...

Bruce Boatman:

Email Message: It's missions like this, really pushing the bounds of our knowledge that inspire the human mind. Along with Philae, and the LHC, we need more interest and more funding in space exploration and science, especially in a world that is increasingly inward-looking. 

When NASA funding was cut, the dreams and ambition of reaching the stars died. All power to the Pluto mission and Philae in breathing life into these dreams once again!

It's missions like this, really pushing the bounds of our knowledge that inspire the human mind. Along with Philae, and the LHC, we need more interest and more funding in space exploration and science, especially in a world that is increasingly inward-looking. 

When NASA funding was cut, the dreams and ambition of reaching the stars died. All power to the Pluto mission and Philae in breathing life into these dreams once again!

The cows in the nearby fields will be blissfully unaware but this tracking station near Canberra, Australia, will be one of the first places on Earth to receive signals and images from New Horizons...

Science Photo LibraryCopyright: Science Photo Library

Sometimes getting out of bed at 4am to do live broadcasts can be a bit of a chore... But not on #PlutoFlyBy day!!!

Scientists here at mission HQ have been dreaming of going to Pluto since the late 80s - and now at last they are very nearly nearly there. And of course, the media get to turn up for the best bit.

I'm looking forward to the countdown to closest approach. And then even more to the signal, hours later, that shows the flyby has been a success.

New Horizons has made its final contact with Earth before the flyby - and set off to make history!

The probe's antenna is now facing away from us and for the next few hours it will be going through a pre-programmed series of manoeuvres.

Quote Message: Only when New Horizons has its trove of images safely in its onboard memory will it call home again. This is not expected to happen until just after midnight (GMT) into Wednesday. It means there will be a long, anxious wait for everyone connected with the mission, as they hold out for a signal that will be coming from almost five billion km away. from Jonathan Amos Science correspondent, BBC News

Only when New Horizons has its trove of images safely in its onboard memory will it call home again. This is not expected to happen until just after midnight (GMT) into Wednesday. It means there will be a long, anxious wait for everyone connected with the mission, as they hold out for a signal that will be coming from almost five billion km away.

Expect more updates during the day however, as the mission controllers and people all over the world count down to the craft's historic encounter with Pluto!

The probe is now closer to Pluto than our Moon is to Earth. And closing fast - as the mission's official Twitter account makes clear...

This animation (by Dan Durda from the Southwest Research Institute) shows New Horizons from all sides - and gives you an idea of why the spacecraft is sometimes likened to a baby grand piano.

Billy Joel , anyone?

If you're in the UK, turn on your TV (or click here) at 22:30 BST to watch Newsnight.

Our science correspondent Rebecca Morelle and producer Stuart Denman have been hard at work making a little film all about the New Horizons mission.

Tune in and join the excitement!

Charon is Pluto's biggest moon and the other big target of tomorrow's flyby.

Its dark polar region has been baffling scientists as it comes into focus. 

The latest images also show some other features which look like craters and chasms. 

If this is indeed what they are, the valleys would be longer and deeper than the Grand Canyon - quite something on a world less than 800 miles (1,200km) across.

NASA/JHUAPL/SWRICopyright: NASA/JHUAPL/SWRI

New Horizons passed the "one million miles to go” mark in the early hours of Monday (GMT). It’s now under one million km from Pluto, for those of you like me who only really understand “new money”. 

And the clock will run down very rapidly as New Horizons sweeps towards the Pluto system at 14km/s. Closest approach is set for 11:50 GMT (12:50 BST; 07:50 EDT) on Tuesday. 

I wanted to share this mosaic that has been assembled by astro-photographer Damian Peach. It shows the growing disc of Pluto as New Horizons has got closer and closer in recent days.  

NASA/JHU-APL/SWRI – DAMIAN PEACHCopyright: NASA/JHU-APL/SWRI – DAMIAN PEACH

The face that is third from the right is the one that the probe will see as it passes just 12,500km above the surface. The best pictures that come back will have a resolution better than 100m per pixel. 

This means you would be able to discern any football stadiums, if they were present on the dwarf planet. There aren’t any; I’m sure of that. But it gives you a sense of what to expect.

We’re not going to see the very highest resolution pictures immediately after flyby. However, the mission team is promising some spectacularly detailed views. 

Watch out also on Tuesday for the last full-frame view of Pluto to be sent to the ground before New Horizons goes into radio silence for its flyby.

This is a "money in the bank” shot that will have been acquired on Monday. It’s an insurance policy in the highly unlikely event that the probe hits a small piece of icy debris during the flyby and is destroyed.

Because of the radio silence from New Horizons during the flyby, we won’t actually have anything new to show on Tuesday itself. So, Nasa will give us Monday’s "money in the bank” shot to tide us over. 

The steamy heat of a Maryland summer is a surreal setting to wait for news from an icy world on the edge of the solar system. Off the freeway and past the shopping malls, we’re poised for new sights from three billion miles away. It’s vacation time here at Johns Hopkins University but in one corner of an otherwise quiet campus there’s an increasingly excited throng. 

Sometimes when Nasa scientists talk of humanity’s destiny reaching for the stars, it feels uncomfortably over-the-top. But, with this mission, evocative language describing the journey of the robotic New Horizons spacecraft does not seem like hype. We are genuinely on the brink of some major discoveries. Talk of making history, exploring unknown realms, satisfying our eternal curiosity about what lies beyond is not out of place. 

And, for once, bizarrely, there are no real experts. Everyone is a novice when it comes to Pluto and I’m finding people are all asking the same questions for which there are no answers yet. What are the weird-looking features on Pluto’s surface? Will New Horizons survive its flight through a cloud of dust? Does Pluto actually share an atmosphere with its largest moon Charon? 

Hour by hour, we’re all on tenterhooks for images that can only become sharper and more revealing.

NASA/JHUAPL/SWRICopyright: NASA/JHUAPL/SWRI

New Horizons just zipped within one million km of Pluto.

It will cover that distance in less than 20 hours and shoot past the dwarf planet just 12,500km from its surface.

Fly, little probe, fly!

SPLCopyright: SPL

You can check its exact progress here:

http://pluto.jhuapl.edu/

The briefing is over but the work is just beginning for New Horizons.

The team will hear from the little probe once this afternoon and one final time overnight, before it barrels silently past Pluto tomorrow.

That crucial overnight downlink, called "E-Health 1", is due at 04:15 BST. It will include the last pre-flyby picture of Pluto. 

At less than 4km per pixel, it will (again) be our clearest ever view of the dwarf planet. Hopefully the team will show it to us tomorrow, as we celebrate the flyby taking place.

Principal investigator Alan Stern told the briefing room there was "a tremendous energy" on the New Horizons team at the moment.

For eight years - ever since it swung past Jupiter - the probe has been traversing empty space. It crossed the orbits of Uranus and Neptune when they were on the other side of the Solar System. 

NASACopyright: NASA

Quote Message: People talk a lot about how surreal it is that we're actually here - that we've reached the target. For myself, it feels like you've been walking on an escalator for about a decade, and then you step onto a supersonic transport. The energy is just electric. from Prof Alan Stern Principal investigator, New Horizons

People talk a lot about how surreal it is that we're actually here - that we've reached the target. For myself, it feels like you've been walking on an escalator for about a decade, and then you step onto a supersonic transport. The energy is just electric.

Two other pieces of news. Composition data confirms the northern polar cap of Pluto is made of nitrogen and methane ices. Also, New Horizons is detecting nitrogen coming off Pluto's atmosphere. This is expected, but not quite so early in the approach phase. It means Pluto is losing higher volumes - or it is losing them more efficiently than previously modelled.

It is one of the big goals of the mission to understand how the thin, wispy atmosphere comes off Pluto, because the loss process will be similar to the one that affected the Earth very early in the history of the Solar System. It was already thought that Pluto lost a few hundred kg of atmosphere every second. Somehow it must replace this because at that rate, all the atmosphere would be gone in roughly 10,000 years. It's a fascinating world.

With the data that's already been streaming in from New Horizons, scientists have finally managed to nail down Pluto's size. And it turns out it's bigger than they thought - a radius of about 1185km, plus or minus 10km.

Now, compared with the classical planets it's still puny; with its big moon Charon it could squeeze into an area the size of the US.

But it is a different story when you look at the Kuiper Belt, the patch of space where it resides. It looks like Pluto has now been confirmed as the biggest object there - so King of the Kuiper it is!

The media have piled into one of the auditoria here at the Johns Hopkins University Applied Physics Lab for the first of the big set-piece briefings on the Pluto flyby. And we start with some new results.

Alan Stern, the principal investigator on the New Horizons probe, announces the best estimate yet of Pluto's radius. He puts it at 1,185km plus or minus 10km. That's a diameter of 2,370km.

That's slightly bigger than we thought, which means the planet is a little less dense than previously stated. It is likely an indication that the fraction of ice in its interior is higher than recognised by our current models.

There is one other big implication: It means Pluto is bigger than Eris, the other Kuiper Belt object whose discovery was partly responsible for Pluto's demotion from full planet status. Eris has a diameter that is about 30km smaller.

And we're still a day away from closest approach! Alan Stern: "Fasten your seatbelts. New Horizons is arriving in the Pluto system."

Dr Cathy Olkin, one of the New Horizons co-investigators, said that when the craft zooms past tomorrow it will be close enough for its cameras to pick out surprisingly small features.

Quote Message: You would be able to identify the ponds in Central Park from Dr Cathy Olkin Planetary scientist, Southwest Research Institute

You would be able to identify the ponds in Central Park

Pluto is slightly bigger than expected, the mission's principal investigator just explained: 2,370km wide (give or take 20km)

That puts it just ahead of the other far-flung dwarf planet Eris.

Stern also said that Pluto definitely has ice caps - consisting of frozen nitrogen and methane.

Click on the "live coverage" tab above to tune in to Nasa TV and hear the latest from the New Horizons team.

Dr Paul Shenk, a mission scientist from the Lunar Planetary Institute, has been speaking to journalists, who have tweeted some of his comments. 

He is also reported as saying that:

• the dark, twisting lines seen in the new Pluto pictures could be eroded craters or fracture lines, but nobody is certain
• the absence of very big craters suggests the surface might be very "young"
• eventually, the New Horizons data will be able to reveal hills as small as 100m

Sometimes when there's no studio available, a blanket has to do!

Some brand new images have been uploaded to the mission page on the website of Johns Hopkins University Applied Physics Laboratory.

They show both Pluto and Charon from a distance of about three million km; they were snapped late on Saturday evening and downlinked from New Horizons just last night.

Taken in black-and-white by the LORRI camera, they will help the team to make any final navigational adjustments - as well as offering yet another best-ever view of the dwarf planet!

NASA/JHU-APL/SWRICopyright: NASA/JHU-APL/SWRI

NASA/JHU-APL/SWRICopyright: NASA/JHU-APL/SWRI

You can see the full set here - the first five images are new:

http://pluto.jhuapl.edu/soc/Pluto-Encounter/index.php

Nasa TV will be streaming live briefings at the important stages over the next couple of days. 

You will be able to watch the key broadcasts right here on this page! These will be as follows, in British Summer Time:

• Monday 15:30 - briefing on mission status and what to expect
• Tuesday 12:30 - countdown to "closest approach"
• Tuesday 13:00 - briefing and release of final pre-flyby image
• Wednesday 01:30 - waiting for New Horizons to "phone home" 
• Wednesday 02:30 - briefing on mission status

It's worth remembering that throughout Tuesday, we won't hear anything from New Horizons itself - it'll be too busy taking pictures and measurements.

In a container bolted to the side of New Horizons, there is a portion of the ashes of Clyde Tombaugh, who first discovered Pluto in 1930.

APCopyright: AP

In this video, some of Tombaugh's relatives talk to Nasa about his legacy.  

The BBC has a team of experts at the operations centre, at Johns Hopkins University in Baltimore, ready to give you the latest.

Sky at Night presenter Dr Chris Lintott is among them, and already getting excited...

Hello! In almost exactly 24 hours' time, Nasa's New Horizons spacecraft is due to hurtle past Pluto. 

On this page we'll keep you up-to-date with all the latest developments.

It's the culmination of a 10-year, five-billion-km journey, so you won't want to miss it!

NASACopyright: NASA