Just thirteen light years away, a red dwarf star is speeding away from us, towing along two rocky planets with it. One of these, five times the size of earth and twice as old, lies in the habitable zone. That means conditions seem to be right for liquid water to exist. This is the nearest planet in a habitable zone discovered till now and scientists are excited at the prospects.
The red dwarf star, called Kapteyn after its 19th century Dutch discoverer is a cool, small star—the most common type of star in our galaxy. While our sun is between five and six thousand degrees Kelvin at its surface temperature, Kapteyn's surface is more like 3500 degrees K. It is about a third the size of our sun. But it is estimated to have been formed right around the time the universe itself was born some 13.8 billion years ago. So it is very ancient.
Kapteyn and other such primordial stars live in a halo just beyond the inner boundary of our galaxy, forced out of wherever they formed by immense galactic forces. Hence Kapteyn is speeding away from Earth at 245 km per second.
Twenty astronomers on three continents combined ten years of data from three large large telescopes to pinpoint two planets circling this fleeing star. They are called Kapteyn b and c, orbiting with periods of 48 and 120 days, respectively.
"We were surprised to find planets orbiting Kapteyn's star," said lead author Dr. Anglada-Escude from Queen Mary University of London's School of Physics and Astronomy. "Previous data showed some moderate excess of variability, so we were looking for very short period planets when the new signals showed up loud and clear."
Of the two, Kapteyn b is the only one in the habitable zone. Kapteyn c, with at least 7 earth masses, may be a rocky body as well, but astronomers suspect it is too far from the dim red dwarf surface to have liquid water. It remains to be seen is if the atmospheres of either of these planets contains water. Before knowing for certain, astronomers would need to see the planets pass directly in front of their parent star.
Because of their advanced age, their tendency to form rocky planets and the high precision we have achieved in measuring their velocities, red dwarfs like Kapteyn will continue to be objects of interest for planet-hunting astronomers and astrobiologists alike. This is especially true for objects in the galactic halo, which is home to the oldest known star in the Universe: HD 140283, discovered last year and estimated to be as old 14 billion years. Newcomers like our Sun formed much later on in the disk. The Earth, the home of every form of life currently known, is only 4.5 billion years old.
Said Anglada-Escude, "It does make you wonder what kind of life could have evolved on those planets over such a long time.
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