Artist's
impression of five possible planets orbiting the star Tau Ceti,
which is …
Dazzling distant
galaxies
A sun-like star in our
solar system's backyard may host five planets, including one
perhaps capable of supporting life as we know it, a new study
reports.
Astronomers have
detected five possible alien planets circling
the star Tau Ceti, which is less than 12 light-years from Earth — a
mere stone's throw in the cosmic scheme of things. One of the
newfound worlds appears to orbit in Tau Ceti's habitable zone, a
range of distances from a star where liquid water can exist on a
planet's surface.
With a minimum
mass just 4.3 times that of Earth, this potential planet would be
the smallest yet found in the habitable zone of a
sun-like star if it's confirmed, researchers said.
"This discovery is
in keeping with our emerging view that virtually every star has
planets, and that the galaxy must have many such
potentially habitable Earth-sized
planets," study co-author Steve Vogt, of the University of
California, Santa Cruz, said in a statement. "They are everywhere,
even right next door." [Gallery: 7 Potentially
Habitable Exoplanets]
The five planet
candidates are all relatively small, with minimum masses ranging
from 2 to 6.6 times that of Earth. The possibly habitable world,
which completes one lap around Tau Ceti every 168 days, is unlikely
to be a rocky planet like
Earth, researchers said.
"It is impossible
to tell the composition, but I do not consider this particular
planet to be very likely to have a rocky surface," lead author
Mikko Tuomi, of the University of Hertfordshire in England, told
SPACE.com via email. "It might be a 'water world,' but at the
moment it's anybody's guess."
Spotting
signals in the noise
Tau Ceti is
slightly smaller and less luminous than our sun. It lies 11.9
light-years away in the constellation Cetus (the Whale) and is
visible with the naked eye in the night sky. Because of its
proximity and sun-like nature, Tau Ceti has featured prominently in
science fiction over the years.
Astronomers have
searched for exoplanets around Tau
Ceti before and turned up nothing. But in the new study,
researchers were able to pull five possible planetary signals out
from under a mountain of noise.
Tuomi and his team
re-analyzed 6,000 observations of Tau Ceti made by three different
spectrographs, instruments that allow researchers to detect the
tiny gravitational wobbles orbiting planets induce in their parent
stars.
The three
instruments are the High Accuracy Radial velocity Planet Searcher
(HARPS), on the European Southern Observatory's 3.6-meter telescope
in La Silla, Chile; the University College London Echelle
Spectrograph (UCLES) on the Anglo-Australian Telescope in Siding
Spring, Australia; and the High Resolution Echelle Spectrometer, or
HIRES, on the 10-meter Keck telescope atop Mauna Kea in Hawaii.
Using new analysis
and modeling techniques, the team spotted the five faint signals,
successfully separating them from noise caused by stellar activity
and other factors.
"We pioneered new
data modeling techniques by adding artificial signals to the data
and testing our recovery of the signals with a variety of different
approaches," Tuomi said in statement. "This significantly improved
our noise modeling techniques and increased our ability to find
low-mass planets."
The new analysis
methods should aid the search for small planets, allowing more and
more of them to be spotted throughout the galaxy, researchers said.
[A Galaxy Full of Alien
Planets (Infographic)]
A nearby
planetary system?
The five planets
remain candidates at this point and will not become official
discoveries until they're confirmed by further analysis or
observations. And that's not a sure thing, researchers said.
"I am very
confident that the three shortest periodicities are really there,
but I cannot be that sure whether they are of planetary origin or
some artifacts of insufficient noise modelling or stellar activity
and/or magnetic cycles at this stage," Tuomi said, referring to the
potential planets with orbital periods of 14, 35 and 94 days
(compared to 168 days for the habitable zone candidate and 640 days
for the most distantly orbiting world).
"The situation is
even worse for the possible habitable zone candidate, because the
very existence of that signal is uncertain, yet according to our
detection criteria the signal is there and we cannot rule out the
possibility that it indeed is of planetary origin," he added. "But
we don't know what else it could be, either."
If the Tau Ceti
planets do indeed exist, their proximity would make them prime
targets for future instruments to study, researchers said.
"Tau Ceti is one
of our nearest cosmic neighbors and so bright that we may be able
to study the atmospheres of these planets in the not-too-distant
future," James Jenkins, of the Universidad de Chile and the
University of Hertfordshire, said in a statement. "Planetary
systems found around nearby stars close to our sun indicate that
these systems are common in our Milky Way galaxy."
If confirmed, the
Tau Ceti planets would not be the closest exoplanets to Earth. That
title still goes toAlpha Centauri Bb, a
roasting-hot, rocky world recently spotted just 4.3 light-years
away, in the closest star system to our own.
The new study has
been accepted for publication in the journal Astronomy &
Astrophysics.
