Sunday, June 22, 2014

Exoplanet Duo Orbits A Nearby Ancient Kapteyn's Star

Alien worlds are exoplanets that circle stars beyond our Sun. For a generation now, planet-hunting astronomers have been spotting these very remote worlds, and have found that while some bear an almost eerie resemblance to the eight familiar major planets that dwell in our own Solar System, others are so bizarre that they are unlike anything astronomers ever dreamed of seeing.

In June 2014, an international team of astronomers reported their discovery of a delightful duo of planets circling a nearby and very ancient star known as Kapteyn's Star. One of these newly discovered planets circles within its parent star's habitable zone, which is that "just right" Goldilocks distance for water to exist on its surface in its life-sustaining liquid state. Where there is liquid water, the possibility--though not the promise--of life exists as well. The study has been accepted for publication in the Monthly Notices of the Royal Astronomical Society.

Named for the Dutch astronomer Jacobus Kapteyn, who discovered it towards the close of the 19th century, Kapteyn's Star is very speedy. In fact, it is the second fastest-moving star in the sky, and is a denizen of the our Milky Way's galactic halo, which is an extended cloud of stars that circle our Galaxy in extremely elliptical orbits. Kapteyn's Star is a red dwarf sporting only one-third the mass of our Sun, and it can be observed in the southern constellation of Pictor with only an amateur 'scope.

Inner Solar System and Kapteyn's Star

As of June 10, 2014, approximately 1800 remote exoplanets had been detected--including 1795 planets dwelling in 1114 planetary systems that also includes 461 multiple planetary systems. In January 2013, a group of astronomers announced that their findings indicated that our Milky Way may host as many as 400 billion exoplanets, with almost every star being circled by at least one planet!

The once crippled Kepler mission space telescope has also spotted a few thousand exoplanet candidates--of which approximately 11% could prove to be false-positives. On February 26, 2014 NASA announced the discovery of 715 newly verified exoplanets circling 305 stars using the Kepler Space Telescope.

It is estimated that perhaps 1 in 5 Sun-like stars hosts an "Earth-sized" planet within its habitable zone, and the nearest would therefore be expected to dwell within 12 light-years of Earth. There could also be as many as 40 billion Earth-sized exoplanets circling within the habitable zones of both Sun-like stars and red dwarfs--such as Kapteyn's Star. Red dwarf stars are less massive than our Sun--in fact, they are the smallest true stars dancing around in our Galaxy, as well as by far the most numerous.

The first discovery of exoplanets occurred back in 1992, and these bizarre worlds did not circle a star like our own Sun. In fact, they circled a "dead" stellar relic called a pulsar, which is a speedily spinning neutron star that sends forth gleaming lighthouse-like beacons into interstellar space at very regular intervals. Pulsars are the sad remains of a massive star that perished in the brilliant incandescent fury of a supernova explosion, after it had consumed its necessary supply of life-sustaining nuclear fuel--needed to feed its nuclear-fusing furnace. The pulsar planets are not life-friendly little worlds. In fact, they are downright hostile, and are constantly being showered with the deadly radiation that is persistently hurled out by their bizarre stellar host.

The first discovery of an alien world in orbit around a Sun-like star came three years later, with the detection of 51 Pegasi b, an enormous "roaster"--a hot Jupiter planet that hugged its parent star, 51 Pegasi, in a very close, fast orbit.

For more than two decades, planet-hunting astronomers have discovered a virtual treasure trove of unearthly delights--strange, wonderful, and sometimes almost disturbingly familiar alien planets, that are the distant members of planetary families belonging to stars beyond our Sun.

Kapteyn's Planets

The international team of astronomers, led by Dr. Guillem Anglada-Escude of Queen Mary University of London in the UK, reported on the two new planetary discoveries in orbit around the very ancient Kapteyn's Star. One member of this fascinating duo, dubbed Kapteyn b, is potentially habitable because it sports both the right orbit and size to sustain precious liquid water on its surface. What makes this discovery particularly interesting is the strange history and age of the host star. Kapteyn b is probably more than twice as old as Earth, and it is the oldest known potentially habitable alien world listed in the Habitable Exoplanets Catalog.

Kapteyn b is a "super Earth" that circles its speedy stellar parent every 48 days, and sports a hefty mass of at least five times that of our planet. The second planet, Kapteyn c is a somewhat heavier "super Earth", that circles its star in a wider orbit of 121 days--and is too cold to support liquid water and, hence, life as we know it. Only a handful of properties of the two planets are currently known: minimum masses, distances from their parent star, and their orbital periods. By measuring their atmospheres with technologies made available in the future, astronomers will try to discover whether some of these alien worlds are truly habitable.

Kapteyn b Compared To Earth
The team of astronomers used new data derived from the HARPS Spectometer at the European Southern Observatory's La Silla observatory, the Planet Finding Spectrometer at the Magellan Las Campanas Observatory in Chile, and the HIRES spectrometer at the W.M. Keck Observatory in Hawaii to calculate minute periodic alterations in the movement of the star, resulting from the gravitational tug of the circling planets. Using the Doppler effect, which shifts the star's light spectrum depending on its velocity, the astronomers were able to determine some of the properties of this planetary duo, such as their masses and orbital periods. The Doppler shift method was the original method used to detect exoplanets.

Dr. Steven Vogt of the University of California at Santa Cruz, and his longtime collaborator, Dr. R. Paul Butler of the Carnegie Institution for Science, have been gathering precision radial velocity data of Kapteyn's Star for over a decade at the Keck Observatory. "The discovery of planets around this star is the hard-won fruit of many years of patient, careful acquisition of high-precision data from the HIRES instrument at Keck," Dr. Vogt commented in a June 3, 2014 University of California at Santa Cruz Press Release.

Dr. Anglada-Escude noted in the same Press Release that "We were surprised to find planets orbiting Kapteyn's Star. 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."

Typical planetary systems spotted by NASA's Kepler mission are situated hundreds of light years away. In contrast, Kapteyn's Star is the 25th nearest star to our own Sun, and dwells a "mere" 13 light-years away from Earth. But what makes this discovery particularly special, however, is the captivating history of the star. Kapteyn's Star was born as a sparkling member of a doomed dwarf galaxy that was disrupted and then absorbed by our large barred-spiral Milky Way Galaxy long ago. This galactic disruption event is what shot the star into its extremely speedy orbit in our Milky Way's halo.

The probable relic core of its original dwarf galaxy is called Omega Centauri. Omega Centauri is a strange and enigmatic globular cluster that dwells 16,000 light-years from our planet, and is set on fire by the ancient sparkle of stars that are about as elderly as Kapteyn's Star. Globular clusters are large, compact, spherical stellar clusters that are normally inhabited by a collection of very old stars that dance around in the outer limits of a galaxy.

The ancient stars dwelling in Omega Centauri indicate that the most likely age of the Kapteyn's Star's planetary duo is about 11.5 billion years--which makes them about 2.5 times older than our own planet, and a "mere" 2 billion years younger than the Universe itself. Our Universe was born in the Inflationary Big Bang approximately 13.8 billion years ago.

"It does make you wonder what kind of life could have evolved on those planets over such a long time," Dr. Anglada-Escude said in the June 3, 2014 University of California at Santa Cruz Press Release.

The discovery team of international astronomers includes 24 scientists from nine institutions in six countries.

References and Information:

Kepler Space Telescope

Royal Astronomical Society

Oldest Known Potentially Habitable Exoplanet Found

About the Author:

Judith E. Braffman-Miller is a writer and astronomer whose articles have been published since 1981 in various newspapers, magazines, and journals. Although she has written on a variety of topics, she particularly loves writing about astronomy because it gives her the opportunity to communicate to others the many wonders of her field. Her first book, "Wisps, Ashes, and Smoke," will be published soon.

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