National Geographic

Super Earths Found Circling Ancient Star

This artist's concept illustrates a young, red dwarf star surrounded by three planets.  Kapetyn's Star is similar with its two new-found super-Earth planets, one of which may be hospitable to life.  Credit:  NASA/JPL-Caltech
Artist’s concept of a young red dwarf star surrounded by three planets. Kapteyn’s star is similar, with its two newfound super Earth planets, one of which may be hospitable to life.  Courtesy of NASA/JPL-Caltech

Ancient aliens among us? No, not here on Earth, but maybe circling a dim old star right here in our own stellar neighborhood.

An international team of astronomers reports the discovery of two new planets orbiting Kapteyn’s star, a nearby red dwarf with a long history. One of its newly discovered worlds, dubbed Kapteyn b, circles the star at the right distance to allow seas to survive on its surface, where water is seen as a key ingredient of life as we know it.

The astronomers spotted the planets from the La Silla Observatory and the Las Campanas Observatory, both in Chile, with help from the W. M. Keck Observatory in Hawaii. To make the discoveries, they measured tiny periodic wobbles of the star as its planets gravitationally tugged at it. From these periodic wobbles, the scientists figured out the masses and orbital times of the planets.

Artistic representation of the potentially habitable exoplanet Kapteyn b as compared with Earth. Credit: PHL @ UPR Arecibo
Depiction of the potentially habitable exoplanet Kapteyn b compared with Earth. Courtesy of  PHL @ UPR Arecibo

It turns out that Kapteyn b possesses at least five times Earth’s mass and has a year only 48 Earth-days long. It circles closer to the star than Mercury orbits the sun in our own solar system. But because its star is a cool red dwarf, the planet likely bathes in just enough heat to keep water in a liquid state on its surface.

The second planet, Kapteyn c,  however, is more massive and takes 121 days to circle its host star. The team believes that it lies outside of the  star’s habitable zone, where water would simply freeze.

This artist’s concept shows a planet orbiting a red dwarf star similar to Kaptyen's Star. NASA
This artist’s concept shows a planet orbiting a red dwarf star similar to Kapteyn’s star. Courtesy of NASA

Storied Star

Named after Jacobus Cornelius Kapteyn, the Dutch astronomer who discovered it, Kapteyn’s star resides only 13 light-years from Earth and ranks as the 25th nearest one to our sun.

It belongs to a stellar class known as red dwarfs, or M dwarfs. A fraction of the size of our sun, they shine in the much cooler, red part of the spectrum and appear to be the most numerous type of star by far in our Milky Way galaxy, easily numbering in the billions.

“Finding a stable planetary system with a potentially habitable planet orbiting one of the very nearest stars in the sky is mind-blowing. This is one more piece of evidence that nearly all stars have planets, and that potentially habitable planets in our galaxy are as common as grains of sand on a beach,” said Pamela Arriagada, the second author, and a Carnegie postdoctoral researcher.

And while its classification may be humdrum, the origin of Kapteyn’s star is unusual, to say the least.

Artistic representation of the potentially habitable world Kapteyn b with the globular cluster Omega Centauri in the background. It is believed that the Omega Centauri is the remaining core of a dwarf galaxy that merged with our own galaxy billions of years ago bringing Kapteyn's star along. Credit: PHL @ UPR Arecibo, Aladin Sky Atlas.
Artistic representation of the potentially habitable world Kapteyn b, with the globular cluster Omega Centauri in the background. Courtesy of PHL @ UPR Arecibo, Aladin Sky Atlas

This diminutive star—weighing in at only one-third the mass of our sun—is the second fastest moving star ever recorded. This suggests it may have originated in a dwarf galaxy cannibalized by our much larger Milky Way galaxy some 11.5 billion years ago. The likely remnant core of that long dead dwarf galaxy is a giant globular cluster called Omega Centauri, which contains a mass of hundreds of thousands of stars some 16,000 light-years away.

This storied pedigree would make Kapteyn’s star and its family of worlds some two-and-a-half-times older than Earth, making this super-Earth world, Kapteyn b, the oldest potentially habitable planet yet found.

On a cautious note, a separate team led by Ofer Cohen of the Harvard-Smithsonian Center for Astrophysics reported on Monday that red dwarfs might subject planets to much harsher space weather than the sun deals out to Earth. That would make habitable-zone planets circling red dwarfs more Mars-like, the team reported at the ongoing American Astronomical Society meeting in Boston.

Nevertheless, “it does make you wonder what kind of life could have evolved on those planets over such a long time,” said Guillem Anglada-Escude, part of the Kapteyn b discovery team and an astronomer at the Queen Mary University of London.

This work is published in the latest edition of the Monthly Notices of the Royal Astronomical Society.

See for Yourself

Like other red dwarf’s littering the heavens, Kapetyn’s star is too faint to be seen with just the naked eye at 8.9 magnitude. However it’s an easy target for binoculars from a dark sky or small telescope in the suburbs.

Skychart showing locatino of Kaptyen's Star as seen in the southwest evening sky in the Southern Hemisphere. Credit: SkySafari
Skychart showing location of Kapteyn’s star as seen in the southwest evening sky in the Southern Hemisphere. Credit: SkySafari

Located in the small southern constellation of Pictor, this red dwarf is best seen from the Southern Hemisphere.

This time of the year, it can be seen after nightfall using low magnification and wide-field eyepiece about midway up the southwest sky. The distinctively red-hued star is wedged between the constellations Dorado and Columba.


Follow Andrew Fazekas, the Night Sky Guy, on TwitterFacebook, and his website.


  1. Tree frog
    June 6, 3:29 pm

    I’ve been there and I don’t recommend it, the aliens are rude and the food is terrible.

  2. Greg
    June 5, 10:51 pm

    There is a good deal of potential for life on this planet, albeit of the microscopic variety. The Cohen article is a bit overhyped but still a sobering reminder of the possibility that a Red dwarf system can be sterile due to flare activity. Te flip side is that red dwaf star flare activity wanes significantly with age and the planet’s surface can be replenished with organic elements from the outer solar system. The size of the planet makes it likely that it has a strong magnetic field which would help shield it from much of the flare radiation. The big downside here is that the mass is high enough that this planet could have a predominantly hydrogen-helium atmosphere not conducive to life as we know it. Since radial velocity was used to detect it, the diameter is not known which would help pin down what type of atmosphere it really has. If we are lucky and the orbital plane is lined up right, a telescope like Kepler may be able to detect it transiting and then we would know. Such a telescope called TESS is slated for launch by NASA ins 2017.

  3. Lape
    June 5, 7:21 am

    The other problem being that it would take voyager 1 about 214,000 years to reach it… soo umm humans won’t be reaching that anytime soon I presume..

  4. Athanasia Vardakis
    June 5, 2:37 am

    Whatever the outcome of this potentially habitable planet is – I am quite amazed at the great work of astronomers! Keep looking guys! How great would it be to be able to expand throughout the universe in the future! (Hopefully we’ll take care of every planet we reach though)!!!!

  5. rafeeq ali manalody
    Saudi Arabia
    June 5, 1:19 am

    is this guys just trolling?

  6. zjloop
    somewhere in the Mars
    June 5, 12:50 am

    It’s really a encouragous things and maybe humankind will find a new environment outside the earth where we can be there. As to whether we can finally find it or not. Be try ,that is the best way to our human’s offspring in the future. The earth is not the permanent home after all I think.

  7. Raphael Mawrence
    Santa Cruz, CA
    June 5, 12:19 am

    I personally think it is quite interesting. Regardless of whether or not there is life within this universe, this is the most fascinating time in scientific history. We discover new things every single day. It is the questioning of this environment that has led us this far and will keep us moving into the future.

  8. Salvador Torres
    Some where on earth.
    June 4, 12:21 pm

    Hmmm, if people are going to try to go to that planet it will be a bad idea because earth was perfectly designed for life, as of other planets they just help our environment on space.

  9. David Keller
    June 3, 10:52 pm

    Sound like someone is falsely trying to make people think that there is alien life at hand. Seeing as the Bible is true, if aliens exist, good aliens have no buisness coming to a fallen world. Bad aliens are bad aliens. But it is probable that alien sighting are demonic manifestations designed to decieve people.