Kapteyn's
star and its planets likely come from a dwarf galaxy now merged with
the Milky way. Bottom right panel shows characteristic streams of stars
resulting from such a galactic merging event. Credit: Victor Robles, James Bullock and Miguel Rocha University of California/UCI, Joel Primack/UCSC. Hi-Res PNG
MAUNA KEA, HI -- An
international team of scientists, led by astronomers at Queen Mary University
of London, report of two new planets orbiting Kapteyn’s star, one of the oldest
stars found near the Sun. One of the
newly-discovered planets could be ripe for life as it orbits at the right
distance to the star to allow liquid water on its surface. The paper is being
published by the Monthly
Notices of the Royal Astronomical Society on June 4.
Dutch
astronomer Jacobus Kapteyn discovered the star at the end of the 19th
century. It is the second fastest moving star in the sky and belongs to
the galactic halo, an extended cloud of stars orbiting our galaxy. With a
third of the mass of the sun, this red-dwarf can be seen in the
southern constellation of Pictor with an amateur telescope.
The
astronomers used new data from the 3.6 meter La Silla Observatory in
Chile to measure
tiny periodic changes in the motion of the star, and followed up with
two more
high-precision spectrometers to secure the detection: W. M. Keck
Observatory's HIRES instrument installed on the 10-meter Keck I
telescope on the summit
of Mauna Kea, and PFS at the
6.5 meter Las Campanas Observatory in Chile.
Using
the Doppler Effect, which shifts the star’s light spectrum depending on its
velocity, the scientists can work out some properties of these planets, such as
their masses and periods of orbit.
“We were surprised to find planets orbiting Kapteyn’s
star,” said Dr Guillem Anglada-Escude, from QMUL’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.”
"Paul Butler and I have been
obtaining precision radial velocity data of Kapteyn's star for over a decade at
Keck, and were thus heavily invested in this work,” said Steve Vogt, a
professor of astronomy at the University of California, Santa Cruz that
contributed the data from Keck Observatory. “This quite southerly star was
quite a tough stretch though from Keck, as the star never gets higher than 26
degrees altitude. Fortunately, Mauna Kea has excellent seeing and a clear view
all the way to the southern horizon.”
“The discovery of planets
around this star are the hard-won fruit of many years of patient, careful
acquisition of high precision data from the very stable HIRES instrument on
Keck,” said Paul Butler, astronomer with Carnegie Institution for Science that
works with Vogt. “Our success was also due, in no small part, to the efforts of
the excellent Keck staff that keep this complex facility finely-tuned year in
and year out.”
Based on the data collected,
the planet Kapteyn b might support liquid water as its mass is at least five
times that of Earth's and orbits the star every 48 days. The second planet,
Kapteyn c is a massive super-Earth in comparison: its year lasts for 121 days
and astronomers think it’s too cold to support liquid water.
At the moment, only a few
properties of the planets are known: approximate masses, orbital periods, and
distances to the star. By measuring the atmosphere of these planets with
next-generation instruments, scientists will try to find out whether they can support
liquid water.
Typical planetary systems
detected by NASA's Kepler mission are hundreds of light-years away. In
contrast, Kapteyn's star is only 13 light years away from Earth and is the 25th
nearest star to the Sun.
Kapteyn's star was born in a
dwarf galaxy absorbed and disrupted by the early Milky Way. This galactic
disruption event put the star in its fast halo orbit. The likely remnant core
of the original dwarf galaxy is Omega Centauri, an enigmatic globular cluster
16,000 light years from Earth which contains hundreds of thousands of similarly
old suns. This sets the most likely age of the planets at 11.5 billion years,
which is 2.5 times older than Earth and 2 billion years younger than the
universe itself (around 13.7 billion years).
“It does make you wonder what kind of life
could have evolved on those planets over such a long time,” Anglada-Escude
said.
"This discovery is very exciting,” said Professor
Richard Nelson, Head of the Astronomy Unit at QMUL, who didn't participate in
the research. “It suggests that many potentially
habitable worlds will be found in the next years around nearby stars by
ground-based and space-based observatories, such as PLATO. Until we have
detected a larger number of them, the properties and possible habitability of
the near-most planetary systems will remain mysterious.”
The W. M. Keck Observatory operates the
largest, most scientifically productive telescopes on Earth. The two, 10-meter
optical/infrared telescopes on the summit of Mauna Kea on the Island of Hawaii
feature a suite of advanced instruments including imagers, multi-object
spectrographs, high-resolution spectrographs, integral-field spectroscopy and
world-leading laser guide star adaptive optics systems.
HIRES (the High-Resolution Echelle
Spectrometer) produces spectra of single objects at very high spectral
resolution, yet covering a wide wavelength range. It does this by separating
the light into many "stripes" of spectra stacked across a mosaic of
three large CCD detectors. HIRES is famous for finding planets orbiting other
stars. Astronomers also use HIRES to study distant galaxies and quasars,
finding clues to the Big Bang.
Keck Observatory is a private 501(c) 3
non-profit organization and a scientific partnership of the California
Institute of Technology, the University of California and NASA.
Below are extra materials produced for this news release and are governed by this Creative Commons liscesne: http://creativecommons.org/licenses/by-sa/3.0/deed.en
- The discovery has prompted renowned science fiction writer, Alistair Reynolds to write a short story. Sad Kapteyn describes the arrival of a robotic interstellar probe reaching Kapteyn's planetary system, and a first exploratory survey of its planets in the far future. Alastair Reynolds worked as an astronomer at the European Space Agency, and later he became a full time science-fiction writer. The story is provided for use of this release only on a non-exclusive basis. Copyright remains to Alastair Reynolds 2014. Read the story.
- Watch this movie simulation representing the galactic merging event that put Kapteyn star on its peculiar galactic orbit as a halo star. The simulation has been specifically produced to support this news release. Copyright remains to University of California - Irvine : Victor Robles, James Bullock and Miguel Rocha and University of California - Santa Cruz: Joel Primack.
Media Contact:
Neha Okhandiar
Public Relations Manager - Science and Engineering
T: +44 (0)207 882 7927
Email: n.okhandiar@qmul.ac.uk
Steve Jefferson
Communications Officer, W. M. Keck Observatory
T: (808)881-3827
Email: sjefferson@keck.hawaii.edu
Source: W.M. Keck Observatory
