If you happened to be perusing the Interstellar Vacation Brochure, skip the page that hypothesizes a tropical getaway on an alien world orbiting Barnard's Star. It's a con, no such resort exists.
This is according to a recent analysis of the red dwarf carried out by a group of astronomers who studied the "wobble" of the star in the hope of detecting exoplanets within its habitable zone.
The habitable zone around any given star is the region where liquid water would most likely exist. If a planet orbits further away, any water would likely freeze; any closer the water would boil off. These two extremes are bad for life as we know it, but liquid water is quite useful. Therefore, the hunt for exoplanets that orbit their stars in the habitable zone - particularly small, rocky worlds - are of huge interest to astronomers and astrobiologists. Where there's liquid water, there's the potential for life.
In the case of the solar system, the Earth orbits within the sun's habitable zone. Mars can be found at the furthest extent of the zone (the "cold" end) and Venus can be found at the closest ("hot" end) of the zone.
It can be easy to take our habitable situation for granted, but it has been a game of "hit and miss" for exoplanet-hunting missions like NASA's Kepler space telescope and ground-based observatories to seek out other "true" habitable worlds.
Of course, the limits we place on what we consider to be "habitable" could be pretty arbitrary on a universal scale, but the only example we have of a habitable world is Earth, so it makes sense to start looking for other worlds with similar characteristics as Earth. Ultimately, we may start getting some clues as to potential exoplanetary abodes for life.
Our obsession with finding other examples of life in the universe is obviously a potent driving factor behind the search for a much-hyped "Earth 2.0″, but there is another reason we are seeking out strange, new, habitable worlds beyond the solar system - local stars with habitable exoplanets could become very interesting for future interstellar missions. This, in turn, could provide our future civilization a promise of an extra-solar destination for colonization.
One prominent study into interstellar travel used Barnard's Star as a potential target back in the 1970′s. Project Daedalus, a concept developed by the British Interplanetary Society (BIS), looked into designing a fusion-propelled unmanned starship to send to Barnard's Star to reconnoiter its potential planetary system. Barnard's Star is the second-closest star to our sun, located "only" six light-years away. That's our cosmic backyard in galactic scales.
(Project Icarus has since taken over where Daedalus left off.)
But Barnard's Star may not be the best place to think about sending any starship if you're into exoplanet-spotting. Barnard's Star appears to be a barren star system.
A team of astronomers led by Jieun Choi, of the University of California, Berkeley, analyzed 248 precise Doppler measurements of the star in an effort to detect the gravitational tug of any exoplanets in orbit around it. These measurements were harvested from the Lick and Keck Observatories over a 25 year period from 1987 to 2012.
Sadly, there appears to be no habitable worlds orbiting Barnard's Star. "The habitable zone of Barnard's Star appears to be devoid of roughly Earth-mass planets or larger, save for face-on orbits," the researchers conclude in their paper published on the arXiv preprint service (arXiv:1208.2273v1).
For decades, it was thought that Barnard's Star played host to one or more exoplanets with masses larger than Jupiter. Dutch astronomer Peter van de Kamp had studied the star since 1938 claiming that, through the use of astrometry (the study of a star's wobble to detect planetary bodies in orbit), large exoplanets were there. These new findings, using precise Doppler data, don't only rule out the existence of massive worlds, they also discount the existence of smaller worlds within the red dwarf's habitable zone.
Although this is an ongoing field of study it appears that Barnard's Star wouldn't be the best place to plan on an interstellar vacation.
Image: Barnard's Star may be a lonely red dwarf. Credit: ESO/L. Calçada