NASA's WISE Mission Shuffles Sun's Nearest Stellar Neighbors - Forbes

Artist's conception of the binary system WISE J104915.57-531906 with the Sun in the background. Credit: Janella Williams, Penn State University.

For decades, the ten closest stars to our own Sun made up a pretty static list. Ideas about where to send the first interstellar probes tended to focus on the same three or four star systems which all lie well with ten light years.

But in the last few years, deeper and more sensitive infrared surveys of the Sun's local neighborhood has shaken the stellar pecking order.

NASA's WISE spacecraft, in particular, has caused celestial cartographers to redraw their star maps to include recently discovered cooler and lower mass stars and even brown dwarfs. Brown dwarfs are conventionally defined as stellar-type objects from between 13 to 74 Jupiter masses that are simply too small to ignite thermonuclear burning of hydrogen in their cores. However, some brown dwarfs are thought to burn deuterium.

The new third and fourth nearest stellar objects are now known to actually be cool brown dwarfs found last year with WISE (Wide-field Infrared Survey Explorer) mission data.

'I'd like to visit Wise1049-5319 and Wise0855-0714 most because I discovered them,' said Kevin Luhman, an astronomer at Penn State University. Wise1049-5319 is a binary system in which the companions have masses of roughly 50 times the mass of Jupiter, he says, and as far as we know, Wise0855-0714 is a single object with a probable mass between 3 and 10 times the mass of Jupiter.

'Its surface temperature is similar to the North Pole, making it the coldest object seen outside the solar system, probably with clouds of water ice in its atmosphere,' said Luhman. 'If a probe visited either system, one would want it to come within one [Earth-Sun] distance or less to study these brown dwarfs in detail.'

But undoubtedly the first stop would be nearby Proxima Centauri at only 4.2 light years away in the Alpha Centauri star system. As an M-spectral type red dwarf, it remains closest known star to earth, but is widely-separated from Alpha Centauri A & B - the next nearest stars to Earth.

At only 6 light years away, Barnard's star in the constellation of Ophiuchus is the second closest stellar system to Earth. And although this high-velocity red dwarf star has a long history of astronomers who have claimed that it harbors planets. No such detections have thus far been corroborated, however.

The nearest stars are still the G, M, and K spectral types, says Davy Kirkpatrick, an infrared astronomer at Caltech. But when you start getting to twenty down the list in terms of distance, he says, you start picking up L and T brown dwarfs, about the radius of Jupiter, that weren't known to exist 15 years ago.

The key to finding such cool, low luminosity objects has been the advent of revolutionary new infrared detector technology.

'Infrared technology has [progressed] to be able to create ccd chips large enough to survey big pieces of sky in one image-taking session,' said Kirkpatrick. '[Previously] with one pixel detectors, you had to know exactly where you were pointing. With these new infrared detectors things are popping out that we just couldn't see in the visible.'

Why is observing a bigger piece of sky important for detecting such nearby objects?

'Something [new] that's just within a few light years of the sun is already going to be rare,' said Kirkpatrick. 'So, if you're looking for something faint like a brown dwarf, you really have to survey the entire sky to get lucky enough to accidentally point a telescope in the right direction to hit the one or two objects that are close enough for you to detect.'

How many more such objects lie within less than 10 light years?

'It's unlikely that any new L-type objects will be found within 10 light years,' said Luhman. 'But it's possible if one of them happens to be in a crowded area of sky that can make it difficult to spot faint objects like brown dwarfs. And as a result such an object could have been missed in previous searches.' Dreams of sending a probe to study the Sun's nearest stellar neighbors has captured the imagination of anyone who's ever marveled at the bright star Sirius on a clear summer's eve. But at 8.6 light years away, Sirius and its white dwarf companion won't be our first stop.

In fact, as I noted in ' Distant Wanderers,' 'On its present course, some 30,000 years from now, [NASA's Pioneer 10] probe will pass within three light years of Ross 248, an M star 3 parsecs [9.72 light years] away from Earth in Taurus, a winter constellation visible in the Northern Hemisphere's southwestern sky just after sunset.'

When will we ever send a dedicated probe to a nearby star? Who can realistically answer? But if Luhman were designing such a mission he would take a practical approach.

'To make the most of each mission, it's likely that a 'mothership' would deploy dozens of smaller probes after arriving at the system,' said Luhman. '[They would] study various aspects of the [parent] star and its planets; much like the large number of probes we use to explore our solar system.'

Entities 0 Name: Luhman Count: 4 1 Name: Jupiter Count: 3 2 Name: Earth Count: 3 3 Name: Penn State University Count: 2 4 Name: Kirkpatrick Count: 2 5 Name: NASA Count: 2 6 Name: Sirius Count: 2 7 Name: Kevin Luhman Count: 1 8 Name: Brown Count: 1 9 Name: Alpha Centauri A & B Count: 1 10 Name: Proxima Centauri Count: 1 11 Name: Janella Williams Count: 1 12 Name: Alpha Centauri Count: 1 13 Name: Sun Count: 1 14 Name: Davy Kirkpatrick Count: 1 15 Name: North Pole Count: 1 16 Name: Caltech Count: 1 17 Name: Northern Hemisphere Count: 1 18 Name: Barnard Count: 1 19 Name: Ross Count: 1 20 Name: Ophiuchus Count: 1 Related 0 Url: http://ift.tt/1n8Qg5r Title: The Oldest Known Star in the Universe Description: Astronomers have found the oldest star in the Universe. Well, kinda. It's the oldest one we know of. At least the oldest one we know of for which an age has been reliably measured. OK, enough caveats. What's going on? Some stars are young; we see them being born now....

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