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Sunday 14 June 2015

Philae lives, and Is Jupiter a failed star - or a deuterium burning brown dwarf?


Philae lives!
Update: I've heard that this morning CNES director Mr Le Gall reported a second contact from Philae.

Seven months ago the European Space Agency made an a attempt to drop a robotic lander onto a comet. It's mission was to analyse samples of the comet, looking for molecules that might have contributed to the formation of our solar system and the origin of life. It worked...ish. The various mechanisms meant the secure the little probe, called 'Philae' to the comet's surface didn't work as planned, the lander bounced off the surface, did a sort of long 'hop', then anlother, and wound up.. somewhere. A spot on the comets surface, at the base of a cliff, on it's side.

Above: One of the last images sent from Philae, showing the bizzare texture of the comets material. Courtesy of ESA.
Now, this wasn't a disaster by itself, but the combination of the landers angle and the shadow of the cliff made it impossible to get any sunlight, and so it was impossible for the solar poanels to recharge the landers batteries. Attempts to change Philaes position failed, so the team ordered the craft to carry out some basic science, and then the probe went silent.

Above: Comet 67-P. Somewhere on the incredibly tortured landscape the little lander is till fighting the fight to survive. Courtesy of ESA.
Until last night, when the increasing sunlight on the comet finally got bright enough to wake the little robot up, and Philae phoned home. Details are still coming in, but here's what we have heard so far:
  • Philae was in contact with Earth for two minutes
  • It's solar panels are generating around 24 watts of power - a comfortable margin over the 19 watts minimum it needs for two way communication.
  • It isn't where the team thought it would be.
  • Its Twitter account is active again
  • It's internal temperature is a frigid -35 degrees Celsius, but set to rise
All in all great news, and here's hoping the lander is able to continue it's mission. An amazing achievment! If you speak some French, here's a breaking news report...
...and here's a link to the Nature report.

Elsewhere in the Universe:

Does Jupiter burn deuterium?

It's been said a often that Jupiter is a failed star, and like many things that are often said it's almost completely wrong: True, Jupiter has a very star like composition - hydrogen and helium mainly - it is a huge ball of gas just like a star, and its system of moons is very much like a miniature solar system. However if you ask almost any astronomer they will tell you that it is emphatically not a failed star, it's much to small. and it has never shone by nuclear fusion like a star. They'll say the idea that Jupiter could ever be a star is based on the (still very good IMHO) scifi movie 2010:

Real failed stars are known as 'brown dwarfs': These are star like objects in composition, but too small to generate the pressure and heat in their cores that are needed for hydrogen fusion, the process that makes stars shine. They do, however, fuse deuterium - a rarer isotope of hydrogen that can fuse more easily - for a short while in their lives, which makes them glow dimly in the infra red. For this to happen they need to be at least 13 times heavier than Jupiter - because even deuterium needs that much more pressure in a gas-balls core than Jupiter has.

But there's a twist in this tale: Jupiter does, in fact, 'shine' in the infra red, from some unknown heat source. In fact it puts out half again as much heat as it receives from the Sun, and this heat is what drives its terrible storms, like the Great Red Spot. Various mechanisms have been put forward to explain this - residual accretion heat, compression heat, phase changes in the metallic hydrogen ocean thought to make up Jupiter's lower levels.

Above: A NASA sciencecast, explaining what we don't know about Jupiter's innards, and why that's important.

But this week a paper has been released from the University of Calgary, that could mix all this thinking up, describing experiments that show that deuterium can fuse at Jupiter-level pressures if it is mixed into a solid core - and a whole bunch of theories on Jupiter's formation predict that it should have a solid core, deep, deep down. In fact, the debate about whether or not old Jove has a solid core is part of the reason why the JUNO space probe is heading to Jupiter right now.

Above: Make yerself a cuppa, and sit down to enjoy a full blown documentary on the JUNO mission to X-ray Jupiter. Courtesy of NASA/JPL

If this deuterium-fusion really happens it would also explain why some 'hot Jupiter' planets around other stars seem more puffed up than the heat they  get from their star can explain: They are burning  deuterium, and so have more internal heat to inflate themselves.

This is hardly conclusive proof that we should re-label Jupiter a brown dwarf , and declare all missions to Jupiter interstellar expeditions. But it might be an avenue of research that one day leads us to conclude that Jupiter is not quite a star, but still more than just a big planet....Here's the paper.

Elsewhere on the Internet:
Our Baryons are missing
Is a grand solar minimum approaching?
Airbus to build space tug

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