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Thursday, 11 June 2015

On the edge of knowledge: Could Sedna be from another solar system?

As far as mysterious worlds go the dwarf planet Sedna takes the biscuit. In fact it takes whole packs of biscuits: At 1,500 km across it is much too big to be a comet, yet it's hugely elliptical orbit - an 11,000+ year path ranging out to 31 times further away than Neptune - is very much more comet like than planet like.

Above: Sedna, as seen by the Hubble space telescope. this is the best view we have of this strange little world - and there are no exploration missions scheduled to visit it. But maybe that will change.. Courtesy of NASA.
Sedna's surfaceis a mixture of water and methane ice, and is coloured red by the presence of tholins. Tholins are incredibly complex macromolecules that are thought to play a role in the origin of life. And although there're a lot of icy worlds out there, none has an orbit that defies explanation quite the way Sedna's does: How it got onto such an eccentric path has never been fully explained. It has been cited as evidence of an undetected planet, deeper out into the Kuiper belt. It has even been suggested that Sedna might host a subsurface ocean.

But now an explanation has been put forwards that is more exciting than all the rest: A team from the Leiden Observatory have found that the weird orbit of Sedna would be pretty typical of a world that had been captured from the protoplanetary disk of another star system. That would actually make a lot of sense: We're fairly confident that the Sun grew in the neighbourhood of a fairly close packed star cluster, like the Pleiades - so while it was young close encounters with other young stars would have been frequent.
Above: The orbit of Sedna as compared to the rest of the Solar system. Do we smell or something?
The idea is beguiling - although totally unproven - because it would give us a chance to do some interstellar exploration without ever leaving our own solar system: Sedna is part of a family of similar objects called Sednitos, and the sednitos are just about within range of our space craft. It would be an amazing thing to be able to explore the surface of a world from another solar system, and without some huge breakthrough in space drive technology in the near future, this might well be our best chance. But the icing on the cake is that the Leiden team predict there might be nearly a thousand such worlds - each one a frozen snapshot of another solar system's birth. Here's the link to the paper

Elsewhere in the Universe:

More from the Dawn mission - but no answers (yet):

Damn: Ceres still refuses to give the secrets of the mysterious white spots scattered across its surface! The most recent images from the Dawn space probe were taken at the closest altitude yet, 2,700 km. But the white spots are so bright that there's still no detail visible in them,and so no clues to their origin! One thing seems sure - these mysterious white patches, with their incredibly high reflectivity, make Ceres unique in the solar system.

The team continues to release amazing images, showing landslides, fractures, ridges, and mysterious scratch like features on the surface. They've also released a stunning video of what we've sen of Ceres so far:

Lightsail-1 declared a success!

Above: An animation shoeing the different images of the lightsail sail - look closely and you can see the earth visible between the sail's pars in one of them. Courtesy of The Planetary Society.
Despite much drama, repeated losses of signal, battery glitches, and software faults, the Planetary Society has succeeded in opening the experimental solar sail on it's Lightsail 1 test space ship. The tiny draft won't actually do much solar sailing - it'll soon re-enter earths atmosphere and burn up. But the technology has now been tested, potential bugs identified to be fixed and the next launch in 2016 willbe a full blown solar sailing mission. 

Above: Lightsail caught on camera, from the ground. Courtesy of NASA

For that mission they'll need some more cash, so the planetary society is arranging a kick starter to help get them - literally and figuratively - off the ground:

A Japanese mission to the Martian moons:
Rumour has it that Japan will attempt a sample return mission to the moons of Mars early in the 2020's - watch this space....

Elsewhere on the internet:

Galaxy on the edge of the void
Is the universe really accelerating?
The latest data suggest any acceleration of the universe's expansion is only marginal...
Coldest ever molecules created
Gravitational lens used to image distant galaxy..
Uranus and Neptune: Grown from a cosmic traffic jam?

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