Friday 10 April 2015

New Horzions Closes In On Pluto

Our current best images of Pluto, combining multiple images taken with the Hubble Space Telescope. Not very good.
Image Credit: NASA, ESA, and M. Buie (Southwest Research Institute)

When people find out I study astronomy, I generally get one of two reactions: blank looks and an awkward end to the conversation, or a barrage of questions (I prefer this reaction). And one of the most common questions is some variation on "Why isn't Pluto a planet any more?"

Now, I do have an answer for that, which I'll discuss at the end of this post, but I don't want to dwell too long on it as I don't find it particularly interesting. What is exciting is that, in just a few months time, we are finally going to see Pluto up close for the first time.

On 14th July this year NASA's New Horizons spacecraft will fly past Pluto at a relative velocity of 14 kilometres a second (about 31 thousand mph), becoming the first spacecraft to visit the distant space rock. The event will be fleeting, as at that speed it will be impossible to slow down into orbit without using roughly sixty times the spacecraft's mass in fuel. But for a few months, starting in May, the tiny spacecraft will be close enough to Pluto to get better data than we've ever obtained before. 

What will it see? I think that the interesting thing about this mission is that we don't really know. Our best images of Pluto at the moment, obtained using the Hubble Space Telescope are shown above. The mess of light and dark patches ask more questions than they provide answers. Pluto has one of the most varied surface brightnesses in the solar system- those dark patches really are very black, whilst the lighter patches reflect most of the light that fall on them. But we have no idea what the patches are. Mountains and craters? Frozen lava seas like those on the Moon? We will know very soon.

Even less is known about the moons. So far we've discovered five moons around Pluto. The largest moon, Charon, is the biggest moon in relation to its parent body in the solar system- so big, in fact, that it doesn't really orbit around Pluto, instead they both orbit around a common centre of mass, or barycentre. Some of the first images from New Horizons have nicely shown this peculiar cosmic dance:  

Pluto and Charon form a binary system, orbiting around each other in 6.4 days. Image Credit: NASA/APL/Southwest Research Institute

The four other moons, called Nix, Hydra, Kerberos and Styx, are much smaller than Charon and were only discovered recently. Their small size has lead to suggestions that they might be the largest remnants of a cloud of debris, a hypotheses that New Horizons will be able to test. Although hopefully not by flying through it at 14 kilometres a second...

In addition to the first good images of Pluto and its moons, New Horizons will return a wealth of other science data. The spacecraft carries seven instruments, including spectrometers to observe Pluto's surface composition and investigate its tenuous atmosphere, solar wind detectors to see how Pluto interacts with it's distant star, and a student-built and -operated dust counter.

With a whole new world to explore, NASA and the International Astronomical Union (IAU) have asked the public to suggest names for the surface featured New Horizons will find. Until the end of April you can nominate and vote for names here, as long as they fit into a set of categories like historical and fictional explorers or spacecraft. The IAU will then come up with a list of approved names based partly on your votes.

(My favourite fictional spacecraft is probably the Falling Outside The Normal Moral Constraints, which I don't think will make the list somehow. Points if you know where it's from.)

I will almost certainly write more about this mission as the results come in, but I suppose I better address the planet thing now.

For years after Pluto's discovery in 1930, it was the only object bigger than a comet we knew about in the outer solar system, so although it's significantly smaller than any of the other planets  (less than half the diameter of Mercury, the next smallest) its planet status was secure. Problems began to arise with the detection of more objects in what we now know as the Kuiper Belt, with things really becoming unstuck in 2005 when an object larger than Pluto, Eris, was discovered far beyond the Kuiper Belt.

At this point it was clear that the old system of nine planets couldn't last- either Eris and several other objects, including maybe even some moons, had to reclassified as planets, or Pluto had to go. In an infamous meeting in 2006, the IAU decided on the latter. Pluto was stripped of its planet status, joining Eris and a handful of other objects in the newly created dwarf planet class.    

Was this the right decision? Whilst I agree that something had to be done, I'm not sure that the right thing was done. The definition of dwarf planet has many problems, and doesn't work at all when applied to the other solar systems that we're now discovering by the bucketload.

Perhaps we need to stop trying to define things into rigid categories, as it increasingly looks like the Universe isn't like that. Recently we've found plenty of things that don't fit into the old definitions. We've spotted planets bigger than Earth but smaller than gas giants, brown dwarf stars that are small enough to be planets, and asteroids that look like comets. Rather than arguing about arbitrary definitions, maybe we should just keep looking and see what's out there.

The images and data that New Horizons will be far more exciting and interesting that any argument over whether it's a planet or not. With this in mind, I propose that we refer to Pluto from now on as a "Mysterious Round Shiny Dark Ice Rock Thing".

Like my favourite spaceship, I doubt that will get past the IAU.

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Monday 19 January 2015

Near-Misses: Beagle 2 Found And SpaceX Crash A Rocket

A  picture of the surface of Mars obtained by the Mars Reconnaissance Orbiter. The bright patch in the centre is the right shape and in the correct place to be the long-lost Beagle 2 lander. Image Credit: HiRISE/NASA/Leicester

This Friday saw news of two space related near misses- missions that came very close to success, but failed at the last moment. The first was the discovery, after eleven years searching, of the UK-led Mars Lander Beagle 2.

Carried to the red planet by the European Space Agency's Mars Express, the tiny space craft was planned to land on Christmas Day 2003. Although Beagle 2 was both small, around two meters across when fully deployed, and cheap, with a total budget in the region of £50 million, its innovative science payload would have been able to make the kind of observations that are only now being carried out by the two billion dollar Curiosity rover.

Sadly, the lander never called home. With no signal picked up on Earth, it was assumed that Beagle 2 had crashed onto the surface of Mars. Most of the blame was attributed to the complex landing system, which used a sequence of parachutes and airbags to safely lower the lander onto the surface.

But last year something was spotted in images of the landing site taken by the HiRISE camera on NASA's Mars Reconnaissance Orbiter- a bright spot, at odds with the read surface around it. Follow-up images confirmed that the object was really there, and that it probably wasn't just an unusual surface feature. With maximum resolution of around 0.3m, HiRISE was just able to pick out the shape of the bright patch- A shape which matched that of the long-lost Beagle 2.

More images showed that the structure of the bright patch was consistent with Beagle 2 having managed to unfold only two of its four solar panels. Here at last was the explanation for why the tiny spacecraft had never been heard from- the transmitter was blocked by the panels that had failed to open.

If this is Beagle 2, then it reveals that the landing system did work, and that Beagle 2 was the first European spacecraft to successfully land on Mars. Although it is probably better to know what happened, it's not really a happy ending- Beagle 2 came so close to success!

Artists impression of Beagle 2 fully deployed on the surface of Mars. The HiRISE observation appears to show that just two of the solar panels deployed, leaving the crucial transmitter covered up. Image Credit:

The other near miss? On Friday afternoon, SpaceX released this footage of their attempt to land a rocket on a floating platform. I recommend turning the sound up:

The Falcon 9 rocket lifted off on 10th January, carrying a Dragon cargo ship, which successfully docked with the International Space Station a few days later. During the launch, SpaceX attempted something that has never been done before: Landing the first stage of the rocket, which drops off about three minutes into the flight, onto a floating platform in the middle of the Atlantic.

As the video shows, they hit it dead on, landing on the platform within an accuracy of about ten metres. Unfortunately, at the last second the control surfaces of the rocket ran out of hydraulic fluid. The Falcon 9 hit the platform at an angle, causing what SpaceX's founder Elon Musk dubbed a "Rapid Unscheduled Disassembly".

Unlike Beagle 2 though, this isn't the end of the story. SpaceX will try again on their next launch at the beginning of February, this time with more hydraulic fluid. If they can perfect these landings then they will be able to reuse the rocket, slashing the currently huge cost of space travel.

And it's not really the end of the story for Beagle 2. The lessons learnt from the unfortunate spacecraft will go into the next UK-led mission to Mars, the 2018 ExoMars rover.  

Follow me on Twitter for new blog posts. I also wrote an Astrobite this week.

Wednesday 31 December 2014

The Stuff About Space That I Missed In 2014

2014 was a busy year for space exploration. Whilst I've covered a few of the notable stories and discoveries of the year, there have been many more that I've missed for one reason or another. To round off the year then, here is a brief look at four interesting space stories that I missed...

Three images showing the distant 2012 VP113 moving against a background of stars. Image Credit: Scott Sheppard/Carnegie Institution for Science
Whilst I was busy writing about the discovery of rings around the asteroid Chariklo, another discovery in the solar system was vying for attention. The image above shows three observations of the same patch of sky, each taken two hours after the last. Moving against the background of stars is a tiny, yet remarkable dot. 2012 VP113 is no more than a thousand kilometers across, but is currently over 80 Astronomical Units (AU, the distance between the Earth and the Sun) away from the Earth.

It won't get much closer, and will swing out to 240 AU from the Sun at the furthest point in its orbit. That puts it way beyond the orbit of Neptune, the furthest planet from the Sun. Only one other object, Sedna, is in a similar orbit to 2012 VP113. In fact their obits are suspiciously similar, leading the discoverers to suggest that their passage around the Sun could be being shaped by a unseen planet in the far reaches of the Solar System. Or it could be coincidence.  
Artists impression of WISE J085510.83-071442.5, the coldest known "star". Image Credit: Robert Hurt/JPL, Janella Williams/Penn State University
In April astronomers at Pennsylvania State University announced the discovery of a very strange object. WISE J085510.83-071442.5 is a brown dwarf, one of a mysterious, ill-defined class of object that bridge the gap between stars and planets. Using NASA's WISE and Spitzer space telescopes, the discoverers had found that this brown dwarf was not only one of the closest objects to the Sun outside of our Solar system, at just 7.2 light years, but was also the coldest brown dwarf known.

The temperature on WISE J085510.83-071442.5 is between -13 and -18 degrees Celsius, as cold as Earth's poles. The low temperature shows that the object has a mass of around 3 to 10 times that of Jupiter, which is actually a little small for a brown dwarf. In fact it doesn't really fit into any of our current categories of astronomical objects- making it even more interesting.

Lift off of the Soyuz rocket, beginning the ill-fated voyage of the Russian space sex geckos. Image Credit: Roscosmos
"Russian Sex Geckos Lost In Space", or variants thereof, must be in the running for best headline of all time. Last August the Russian space agency, Roscosmos, launched the latest in a series of Foton laboratories, uncrewed spacecraft based on the old Vostock capsules. On board this particular launch were experiments studying the effects of spaceflight on various plants and animals. They included five geckos, sent into space to so see how their behaviour and sexual activity responded to weightlessness.

Disaster struck a few days after launch, as ground controllers lost contact with the tiny spacecraft. Stranded in the wrong orbit, the geckos were at risk of a fiery death in the Earth's upper atmosphere. Contact was restored a few day later, and the mission cut short before anything else went wrong. Sadly, when the capsule was recovered at the beginning of September, all of the geckos were dead. The Foton's heating systems had malfunctioned, freezing the unfortunate space lizards. Hopefully they died having a good time...

Artist's impression of the Kepler spacecraft, along with the different patches of sky that will be the targets of the K2 mission. Image Credit: NASA Ames/JPL-Caltech/T Pyle
Closing out the year was the news that the resurrected Kepler spacecraft has spotted an exoplanet, the first confirmed discovery of its new mission. Launched in 2009, Kepler spent the first years of its life staring at a single patch of sky, looking for tiny dips in the light caused by planets passing in front of their stars.

Although highly successful, with over one thousand planet candidates spotted, this technique relied on the spacecraft being able to precisely control the direction in which it was pointing. Kepler achieved this using four gyroscopes, or reaction wheels. Unfortunately by the middle of 2013 two of the wheels had failed, leaving Kepler at the mercy of the buffeting solar wind.

With a continuation of its original mission impossible, engineers at NASA came up with an ingenious solution to allow the stricken spacecraft to carry on hunting for planets.  The pressure from the solar wind, that would otherwise push it of course, can actually be used to stabilize the spacecraft in certain directions. This new mission, dubbed K2, will see Kepler stare at several patches of sky, remaining at each one for around 80 days.

The first confirmation of a new planet found with this technique was announced on 17th December.  HIP 116454 b has a diameter around two and half times the size of the Earth, with just under 12 times Earth's mass. This probably means that it is a small gas giant, known as a mini-Neptune. Hopefully this will be the first of many planetary discoveries from Kepler's new mission,  

My favourite space image of the year: The Philae lander heads off into the dark towards Comet 67P. Image Credit: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

And that's all I have time to write about! There has been plenty more space stores this year, from the much-hyped but ultimately inconclusive BICEP2 results, interesting findings on Mars by NASA's Curiosity rover and a host of ups and downs for commercial spaceflight. More stuff about space will certainly come in 2015.

New blogs will be posted on Twitter. Happy New Year!

Tuesday 9 December 2014

NASA Sucsessfuly Tests The Orion Spacecraft- But It's Not Going To Mars

A Delta IV Heavy rocket blasts off from Cape Canaveral carrying NASA's Orion Spacecraft on its first, unmanned test flight.
Image Credit: NASA/Bill Ingalls
Warning: There may be opinions ahead...

On Friday the 5th of  December the world watched as the most powerful rocket in the world blasted off from Cape Canaveral, Florida. Atop the bright orange Delta IV Heavy was NASA's new human spacecraft, Orion, making its first flight.

Although there weren't actually any people on it- that won't happen until 2021 at the earliest. This was an uncrewed test flight only, looping around the Earth then boosting out to nearly 6000 km high.

Four hours after launch Orion hit the top of Earth's atmosphere traveling at 32000 kilometers per hour, 85% of the speed it would have had if it it had come back from the Moon. Protected by its heat shield, Orion parachuted down into the Pacific Ocean in a scene reminiscent of the Apollo program.   

The mission was a complete success, testing several of Orion's key systems such as the huge heat shield,  avionics and separation systems. It also looked spectacular, with the whole flight relayed live to Earth via camera on the spacecraft. Those of you who follow me on Twitter will know I was thoroughly enjoying it.

There was one bit I didn't like though. NASA have been promoting this launch as the first step on a "Journey to Mars", part of the agency's aim to land humans onto the Red Planet in the 2030s. But I don't think Orion will ever go to Mars. In fact, at the moment it doesn't look like it's going anywhere.  

Orion drifts down on parachutes: The future of space flight, or a step into the past? Image Credit: NASA
Orion first began development as part of the Constellation program. Announced by George W. Bush after the loss of the Columbia space shuttle in 2003, the plan was to replace the space shuttle with two rockets that would land astronauts on the Moon.  The huge Ares V would do the heavy lifting, carrying the lunar lander and propulsion systems into orbit. A smaller Ares I rocket would then launch carrying Orion, The two parts would then dock in orbit and head off to the Moon.

Constellation looked very good on paper, an Apollo style return to the Moon planned for the early 2020s. Unfortunately it never received enough funding to meet its goals, and it was eventually cancelled in 2010 after just one test flight of a half-finished Ares I.

Instead of a return to the Moon, NASA was ordered to set its sights on Mars. It would turn to commercial companies, such as SpaceX and Orbital Sciences,  to replace the role of the space shuttle in supplying cargo and crew to the International Space Station. This would free NASA up to focus solely on developing the technologies needed to take humans to Mars.

Unfortunately this didn't go down well with a number of US politicians, for whom the cancellation of Constellation would mean severe job losses in the Sates that they represented. After much debate Orion was back, this time to launch on a new rocket, the Space Launch System, cobbled together out of parts left over from the Space Shuttle Program.

But the destination remained Mars, and Orion simply isn't built to do that. It's far too small, no bigger than a large car on the inside. For a journey to Mars, which could take up to a year, a much larger spacecraft will be needed.

NASA have talked about a Deep Space Habitat, a larger spacecraft that would be assembled in orbit to make the journey to Mars- although this is yet to even make it on  to the drawing board. Orion would be used to ferry astronauts up to it, and to bring them home at the end of the voyage.

But in this case it's far too large and expensive, tasked with a job that would be much better suited to the cheaper, purpose built commercial crew ships such as the SpaceX Dragon and Boeing CST100.

Orion has found itself in the worst of both worlds, too small to make the whole journey to Mars and unnecessarily big as a crew transport. And no wonder, as it's perfect for what it was designed to do: Go to the Moon. 

Worse still is its projected time table. Orion is so underfunded that the next test flight isn't until 2018, the first time that the Space Launch System will be ready. And it still wont be carrying any people- the first piloted flight is planned for no earlier than 2021.

NASA doesn't have enough money to build the life support systems yet, so the test flight last week couldn't have carried people even if they'd wanted it to. With up to two new US Presidents between it and its first crewed flight, Orion's chances of ever flying with humans on board are shaky at best.

This isn't to say that we wont go to Mars, or that we can't. I think we should, and will have the technological capability to do so within my lifetime.

But I doubt that Orion will be a part of it.

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Friday 21 November 2014

The First Landing on a Comet

Released from the Rosetta orbiter, the fridge-sized Philae lander drifts down to become the first spacecraft to land on a comet. Image Credit: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA 

And the second, and the third...

At 8.35 GMT last Wednesday morning, five hundred million kilometres from the Earth, a tiny lander called Philae detached from the side of the Rosetta spacecraft. 28 minutes later the signal confirming the separation arrived at ESA’s Space Operation Centre (ESOC) in Darmstadt, Germany. The first ever attempt to land a spacecraft on a comet had begun.

Unlike most spacecraft landings, Philae would not land using rocket engines or parachutes. Rosetta had pushed it away in (it was hoped) just the right direction, at just the right speed to fall gently down onto its target.

The target was Comet 67P/Churyumov–Gerasimenko, an irregular lump of dust and ice less than five kilometres across at its widest point. Separating from Rosetta 22.5 kilometres from the surface, the low gravity of Comet 67P pulled Philae into a leisurely, seven-hour descent. 

As it fell towards Comet 67P, Philae had time to spin round and take a picture of Rosetta...
Image Credit: ESA/Rosetta/Philae/CIVA 
...whilst Rosetta watched Philae disappear into the darkness.
Imaged during its descent by Rosetta's OSIRIS camera in the sequence above, Philae is a 100kg box filled with ten scientific instruments, including cameras, spectrometers, a drill and two labs for analysing surface samples. And, crucially, two harpoons.

These harpoons were to fire as Philae touched down onto the surface of the comet, anchoring itself securely to 67P. The plan had been for a small thruster on the top of the lander to ignite at the same time, holding Philae down onto the surface. But that morning, the team at mission control had discovered that the thruster had stopped working. Only the harpoons could stop Philae from rebounding off the surface of Churyumov–Gerasimenko and back into space.

A picture of the first landing site from 40 meters above the surface. Image Credit: ESA/Rosetta/Philae/ROLIS/DLR
At this point I had to go to a seminar, and spent the next tow hours failing to pay attention to the speaker whilst surreptitiously checking Twitter for news. If Tom Shanks is reading this, then sorry! But I got out in time to celebrate with the rest of the world as, at 16.03 GMT, the signal arrived at ESOC: Philae had landed, the first spacecraft to touch down on a comet. There was much rejoicing.

But the celebrations were short lived. As the mission controllers studied the data relayed back by the orbiting Rosetta, they realised that the crucial harpoons had failed to deploy. Worse still, the signal from the lander was fading in and out, and the power being generated by its solar panels was varying wildly. By the evening, a tentative explanation had been found: Philae had bounced straight off the comet and gone into a spin.

In a series of incredibly detailed images, the orbiting Rosetta spacecraft tracks Philae's wild flight across the surface of Comet 67P. Image Credit: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA
By the next morning the full tale of the landing had been put together. Philae had landed at 15:34 GMT, thudding down in exactly the right place. But without the thruster or harpoons to hold it down, the tiny spacecraft had bounced back up again, heading off the comet at a leisurely 38cm/s. Thanks to the extremely low gravity of 67P, Philae flew over the surface for nearly two hours, flying almost a kilometre high. During that time the comet turned underneath it, the targeted landing site slipping away.

When Philae hit the ground again it made a second bounce, this time for only seven minutes. When it finally came to a halt, the lander was over a kilometre from the spot where it had first touched down. But exactly where Philae had ended up was a mystery.  
Panoramic view of Philae's landing site, with the spacecraft superimposed. It wasn't meant to be this dark... Image Credit: ESA/Rosetta/Philae/CIVA
The first images from the landing site showed a very different place to the flat, sunny target. Philae appeared to be at a tilt, with one leg sicking into space. Worse still, the bulk of the lander's solar panels were in the shadow of a large cliff. If Philae wasn't able to move, then it would only get around 1.5 hours of sunlight each day- nowhere near enough to recharge it's batteries.

But Philae was designed with this scenario in mind. Although the solar panels would have allowed it to carry on working for several months, it had been built with enough battery power to complete all of its initial science observations. While the mission controllers pondered a way to move away from the cliff, Philae's ten instruments swung into action.

The ten scientific instruments Philae used to study the surface of Churyumov–Gerasimenko.  Image Credit: ESA/ATG medialab

The full results from the measurements made by Philae have yet to be released, but a few preliminary discoveries have been announced. Particularly intriguing was the data collected by the Multi-Purpose Sensors for Surface and Subsurface Science, or MUPUS. This instrument deployed a small hammer, deigned to dig into the surface of Churyumov–Gerasimenko and measure the temperature at different depths.

Surprisingly, even at it's most powerful setting, the hammer couldn't make a dent in the surface of 67P. The ground beneath Philae, long expected to be a porous, loosely bound mix of dust and ice, was actually rock-solid. Although this conflicted with accepted knowledge (always a good kind measurement to make), a solid ice crust would explain why Philae bounced so high after its first touchdown. The low density of the comet suggests that, beneath this icy crust, the material of Comet 67P is much less tightly packed.

Another instrument, the Cometary Sampling and Composition Experiment or COSAC, detected signs of organic chemical compounds on the surface of Comet 67P. These carbon-rich compounds, which give the comet its deep black colour, are one of the key reasons we are interested in these icy worlds. It is thought that many of the ingredients needed for life on Earth, such as water and some amino acids, were originally delivered here by impacting comets.

With battery power running low, Philae ran through all of it's remaining scientific instruments, drilling into the surface to collect material for its onboard laboratories, receiving and transmitting radar data from Rosetta to map the insides of the comet, and taking yet more images.

By the time its batteries finally gave out, Philae had achieved all of its planned science operations. Despite the bumpy landing, the mission had been a complete success.  
At 36 minutes past midnight on Saturday morning, mission control at ESOC lost contact with Philae. But there's still hope for the little lander. Just before its batteries gave out, Philae had managed to turn itself, bringing it's largest solar panel out of the shade into the faint sunlight.

As Churyumov–Gerasimenko flies ever closer to the Sun, there's a small chance that Philae's batteries will recharge. We may yet be hearing more from the tiny lander. Even if this is the end of Philae's epic adventure, Rosetta is still in orbit of the comet, continuing to revolutionize our knowledge of these tiny, mysterious worlds.

Note: you my have noticed that I haven't commented on #shirtstorm- it's outside the scope of what I wanted (and feel qualified) to talk about, but I recommend and broadly agree with articles like these on the issue.

Another Note: I've stared writing for Astrobites! These are daily summaries  of recent scientific papers, written by astronomy postgraduate students. The style is a bit more technical than this blog, but it's worth a look if you want to to keep up to date with astronomy research. I'll be writing there once a month, and my first post is here

Follow me on Twitter for new blogs.

Tuesday 11 November 2014

How to Watch the Comet Landing!

On the 12th of November the European Space Agency will make the first ever attempt to land a space probe on a comet. If all goes to plan, the Rosetta orbiter will deploy the Philae lander into a seven-hour drift onto the surface of Comet 67P  Churyumov–Gerasimenko.  I'll do a full blog after the event, but here's some hopefully useful bits and pieces to follow the high point of the Rosetta mission:

The first port of call is the ESA Livestream, where all the major events will be shown and new data announced. If I've made this work right, it should be playing above this paragraph. It can also be found (along with lots of other stuff) on the Rosetta homepage.

Timeline of Philae's seven-hour descent onto Comet 67P. The signal from a successful touchdown should arrive at or after 4pm GMT. Click on the image to enlarge. Image Credit: ESA 
Above are the key points in the landing sequence. A much more detailed version is available here.

Image of Philae's targeted landing site, known as Agilkia. Image Credit: ESA
A bit of a wider view: The image above shows the target landing site on the "head" of Comet 67P. It's been named  Agilka, after an island in the River Nile where the temple from the island of Philae was moved to avoid flooding caused by the building of a dam. Philae was the place where the Rosetta Stone was found.

Apart from the ESA Livestream, the best place to stay up to date with the landing is proably Twitter. I will be tweeting updates and my feed should hopefully be appearing below this paragraph. You should also have a look at #CometLanding.

Good luck Philae!

Friday 7 November 2014

ALMA Spots Planets Forming Around a Young Star

High-resolution image of the protoplanetary disc around HL Tau, a young star roughly 450 light-years from Earth. The image, which was taken by the ALMA telescope, shows gaps and rings in the disc carved out by new-born planets. Image Credit: ALMA (ESO/NAOJ/NRAO) 
This morning the image at the top of this page was doing the rounds on Twitter. I, like several others, glanced at it and initially moved on. I've seen plenty of artist's impressions like it before. It took me a while to realise that this isn't a painting. This is a real image from the ALMA telescope, showing the birth of a solar system.

The image shows a star surrounded by a protoplanetary disc, a huge ring of gas and dust around twice the diameter of Neptune's orbit. Invisible at the wavelengths of light that ALMA sees, the central star is a young object called HL Tau, which is  just a million years old. That might seem old, but our own Sun, which is otherwise quite similar to HL Tau, is 4.6 billion years old. HL Tau is a star at the very beginning of its life.

This makes the disc partly expected, but partly mysterious. For the past few decades most models of how planets form have been based on discs like these, the leftover debris from the cloud that collapsed to form the star.  HL Tau is making planets.

Although the entire process is till not fully understood, the theory suggests that slight irregularities in the disc can cause some areas to become more dense. This makes them clump together, growing from dust into small rocks. As they get larger their gravity gets stronger, pulling in more and more material until they begin to look like small planets or asteroids. These planetesimals begin to collide, combining to eventually form planets.  

The ALMA image is a resounding confirmation of this theory, showing this process in action. The disc has huge gaps in it, gaps which are carved out by newly-forming planets. This is the mysterious part, as the presence of these very well defined gaps, at such a young star, show that the planets must be growing much quicker than many simulations suggest.

Not all of the gaps will have planets in them. Some of them will be formed by resonances. This means that, for example, an area of the disc could be going round the star a certain, precise  number of times in the time it takes a further out planet to go round once.

For example, a dust particle in the disc could be going round the star four times for every time planet, which is further away form the star, goes round once. The planet and the dust will then be lined up at exactly the same place each time the planet goes around the star. The gravity of the planet will give the dust an identical tug or kick each time, moving it out of it's orbit.

As this will happen to all of the dust in the same resonant orbit, eventually a gap is cleared. We see the same behaviour in this Solar System- the many rings of Saturn are shaped and sculpted by moons in resonant orbits. Which of the rings in HL Tau are formed by planets, and which are cleared out orbital resonances, will take more observations to find. The full research paper on this observation is yet to be published, so maybe we'll find out then.

Hubble Space Telescope image of the clouds of star-forming gas and dust around HL Tau. Image Credit: ALMA (ESO/NAOJ/NRAO)/NASA/ESA
HL Tau is in the constellation Taurus, currently visible in the late evening in the Eastern sky, near the Moon. But you wont spot the disc, it's far too small.

This leads to the second incredible part of this image: The resolution. The image was taken by the Atacama Large Millimeter/submillimeter Array (ALMA), a huge array of 43 (and counting) telescopes designed observing in the submilliter wavelength range, between infrared and radio waves. The telescopes are spread out by up to fifteen kilometers, allowing them to take extremely sharp images.

ALMA can distinguish between objects separated on the sky by just 35 milliarcseconds. For comparison, your eye has a resolution of around one arcminute- nearly two thousand times worse. Resolution like ALMA would allow you to see both sides of a penny placed over one hundred kilometers away.

It's this high resolution that has allowed ALMA to see the protoplanetary disc in such exquisite detail, picking out the tracks formed by the new, growing planets. And this is in many ways just a proof of concept, a test of ALMA's capabilities. Hopefully we'll be seeing many more amazing things with this telescope in the future.

New blogs will be posted, as ever, on Twitter.

COMING SOON: Next Wednesday (12th) The Rosetta spacecraft will deploy the Philae lander to make the first attempt to land on a comet. I'll be tweeting and blogging along, and I highly recommend keeping track of, in my opinion, the most exciting space event of the year.