Astronomers said Wednesday that they had discovered a planet composed mostly of
water.
You would not want to live there. In addition to the heat — 400 degrees
Fahrenheit on the ocean surface — the planet is probably cloaked in a crushingly
dank and dark fog of superheated steam and other gases. But its discovery has
encouraged a growing feeling among astronomers that they are on the verge of a
breakthrough and getting closer to finding a planet something could live on.
“This probably is not habitable, but it didn’t miss the habitable zone by that
much,” said David Charbonneau of the Harvard-Smithsonian Center for
Astrophysics, who led the team that discovered the new planet and will reports
its findings on Thursday in the journal Nature.
Geoffrey W. Marcy, a planet hunter from the University of California, Berkeley,
wrote in an accompanying article in Nature that the new work provided “the most
watertight evidence so far for a planet that is something like our own Earth,
outside our solar system.”
Only 2.7 times the size of Earth and 6.6 times as massive, the new planet takes
38 hours to circle a dim red star, GJ 1214, in the constellation Ophiuchus —
about 40 light-years from here. It is one of the lightest and smallest so-called
extrasolar planets yet found, part of a growing class that are less than 10
times the mass of the Earth.
Dr. Charbonneau’s announcement capped a week in which the list of known planets,
including these “super-Earths,” grew significantly.
An international team of astronomers using telescopes in Australia and Hawaii
reported in one paper that they had found three planets, including a
super-Earth, orbiting 61 Virginis, a star in the constellation Virgo that is
almost a clone of the Sun. In a separate paper, they reported finding a planet
somewhat larger than Jupiter at the star 23 Librae. It was the first time, they
said, that a super-Earth had been found belonging to a star like the Sun; the
other home stars have been dwarfs.
And in yet another paper, a subset of the same group reported finding a
super-Earth and probably two bigger planets circling HD 1461, a star in Cetus.
Paul Butler of the Carnegie Institution of Washington, who was involved in all
three papers, said astronomers thought that from one-third to one-half of all
Sun-like stars harbor such super-Earths orbiting at scorching distances much
closer than Mercury is to the Sun.
In the 15 years since the first extrasolar planet was found, more than 400 have
been detected. The field is getting more intense as dedicated planet-hunting
instruments like the Kepler satellite from the National Aeronautics and Space
Administration, due to report a new batch next month, get into the game.
Alan P. Boss, a planetary theorist at the Carnegie Institution of Washington,
said of the planet hunters, “Give them a couple more years and they’re going to
knock your socks off.”
Dr. Charbonneau’s planet, only 1.3 million miles from its home star, is
distinguished by its relative coolness. It bakes rather than roasts, a
consequence of the dimness of GJ 1214, which puts out one three-hundredth the
Sun’s energy. He and his colleagues had set out to search for planets around
such stars, noting that they are more numerous and that it is easier to discern
planets around them.
“There is no question,” Dr. Charbonneau wrote in an e-mail message, “that small
stars provide us with the fastest track to looking for life outside the solar
system.”
His planet-hunting equipment is a bank of eight telescopes called MEarth,
pronounced “mirth,” on Mount Hopkins in Arizona. They are only 16 inches in
diameter, no bigger than those that grace the backyard of many amateur
astronomers. They monitor the light of 2,000 nearby stars, looking for the
regular blips caused when a planets passes by, or transits.
In May, Zachory Berta, a first-year graduate student of Dr. Charbonneau’s,
called the group’s attention to a series of blips in the Ophiuchus star that
seemed to be happening every 1.6 days. If he was right, Mr. Berta said, the next
transit would occur at 6 a.m. on May 13.
Dr. Charbonneau was in Washington later that day preparing for a State
Department dinner when he got a group e-mail message that began: “We have a
winner. Congrats Zach!”
From the drop in starlight, the astronomers could calculate the diameter of the
Ophiuchus planet, known now as GJ 1214b. Then they used a sensitive spectrograph
on a 3.6-meter telescope in Chile to measure its gravitational tug on the star,
thus deriving the planet’s mass. Dr. Charbonneau and his colleagues, using those
two numbers, could calculate the density of the planet.
It was only the second time the density of a super-Earth had been measured,
offering a rare chance for comparative planetology. The first — CoRoT 7b,
discovered last year by the European Corot satellite — turned out to be about as
dense as the Earth, suggesting that it is mostly rock.
The new planet is slightly heavier but significantly larger than the earlier
one, and it is only about one-third Earth’s density.
“What we probably have here is a water world,” said Dr. Charbonneau, explaining
that there are three basic ingredients abundant enough to go into the recipe for
a planet.
They are light gases like hydrogen and helium, rocks like iron and silicates and
so-called volatile materials like water.
The best recipe for the new planet would be a world that is predominantly water,
with small amounts of rock in a core tens of thousands of miles underwater,
surrounded by a suffocating atmosphere. By comparison, Earth is 0.06 percent
water.
Dr. Charbonneau said the weight of the new planet’s presumptive atmosphere that
kept the water liquid rather than just boiling into space. If all such
super-Earths have this type of atmosphere, he and his colleagues write in their
paper, none of them is likely to harbor life. Astronomers would have to redouble
their efforts to seek even smaller planets to find habitable environments.
Dr. Charbonneau acknowledged that a different recipe, with more rock and a very
puffy atmosphere, would also fit the data. That is unlikely, he and other planet
experts say, but the sauna world theory may be soon tested.
The planet is close enough to be studied directly by telescopes on or near
Earth. Indeed, Dr. Charbonneau said his team had already applied for observing
time on the Hubble Space Telescope.
“Our own TV signals,” he said, “have already passed this star.”
November
14, 2008
The New York Times
By DENNIS OVERBYE
A little
more of the universe has been pried out of the shadows. Two groups of
astronomers have taken the first pictures of what they say — and other
astronomers agree — are most likely planets going around other stars.
The achievement, the result of years of effort on improved observational
techniques and better data analysis, presages more such discoveries, the experts
said, and will open the door to new investigations and discoveries of what
planets are and how they came to be formed.
“It’s the tip of the iceberg,” said Christian Marois of the Herzberg Institute
of Astrophysics in Victoria, British Columbia. “Now that we know they are there,
there is going to be an explosion.”
Dr. Marois is the leader of a team that recorded three planets circling a star
known as HR 8799 that is 130 light-years away in the constellation Pegasus. The
other team, led by Paul Kalas of the University of California, Berkeley, found a
planet orbiting the star Fomalhaut, only 25 light-years from Earth, in the
constellation Piscis Austrinus.
In an interview by e-mail, Dr. Kalas said that when he finally confirmed his
discovery last May, “I nearly had a heart attack.”
In scratchy telescope pictures released Thursday in Science Express, the online
version of the journal Science, the planets appear as fuzzy dots that move
slightly around their star from exposure to exposure. Astronomers who have seen
the new images agreed that these looked like the real thing.
“I think Kepler himself would recognize these as planets orbiting a star
following his laws of orbital motion,” Mark S. Marley of the Ames Research
Center in Mountain View, Calif., wrote in an e-mail message elaborating on HR
8799.
More than 300 so-called extrasolar planets have been found circling distant
stars, making their discovery the hottest and fastest-growing field in
astronomy. But the observations have been made mostly indirectly, by dips in
starlight as planets cross in front of their home star or by wobbles they induce
going by it.
Astronomers being astronomers, they want to actually see these worlds, but a few
recent claims of direct observations have been clouded by debates about whether
the bodies were really planets or failed stars.
“Every extrasolar planet detected so far has been a wobble on a graph,” said
Bruce Macintosh, an astrophysicist from Lawrence Livermore National Laboratory
in California and a member of Dr. Marois’s team. “These are the first pictures
of an entire system.”
The new planetary systems are anchored by young bright stars more massive than
our own Sun and swaddled in large disks of dust, the raw material of worlds.
The three planets orbiting HR 8799 are roughly 10, 9 and 6 times the mass of
Jupiter, and orbit their star in periods of 450, 180 and 100 years respectively,
all counterclockwise.
The Fomalhaut planet is about three times as massive as Jupiter, according to
Dr. Kalas’s calculations, and is on the inner edge of a huge band of dust,
taking roughly 872 years to complete a revolution of its star.
Both systems appear to be scaled-up versions of our own solar system, with giant
planets in the outer reaches, leaving plenty of room for smaller planets to lurk
undetected in the warmer inner regions. Dust rings lie even farther out, like
the Kuiper belt of icy debris extending beyond the orbit of Neptune.
“This is a window into what our own solar system might have looked like when it
was 60 million years old,” Dr. Marois said.
Sara Seager, a planetary theorist at the Massachusetts Institute of Technology,
said it was significant that the planets in both cases seemed to be associated
with disks of dust, particularly Fomalhaut, one of the brightest and closest
stars known to be host to a massive disk.
“Fomalhaut is like a Hollywood star to astronomers, so we have some personal
excitement here,” Dr. Seager said. “It feels like finding out that one of your
four closest friends just won the lottery big time”
Alan Boss, a planetary theorist at the Carnegie Institution of Washington, said
the triple-planet system in Pegasus was particularly promising, “as we expect
planets to form in systems in general, whereas spurious background interlopers
will generally appear as single ‘planets.’ ” But he and others cautioned that
much more study of these objects was necessary and that the masses imputed to
them were still highly uncertain.
Being able to see planets directly opens the door to spectroscopic observations
that can help determine the composition, temperature and other physical
characteristics of planets and allow for comparisons with one another and with
their parent stars. Dr. Macintosh said he hoped to train a spectroscope on his
new planets as early as Monday.
The new images are the fruits of a long campaign by astronomers to see more and
more of the unseeable. In particular, it is a triumph for the emerging
technology of adaptive optics, in which telescope mirrors are jiggled and warped
slightly many times a second to compensate for the atmospheric turbulence that
blurs star images.
The problem in seeing other planets is picking them out of the glare of their
parent stars, which are millions of times brighter, at least in visible light.
As a result, planet hunters usually look for infrared, or heat radiation, which
is emitted copiously by planets still shedding heat from the process of
formation.
For their observations, Dr. Marois and his colleagues used the 8-meter in
diameter Gemini North and the 10-meter Keck telescopes on Mauna Kea in Hawaii,
both of which had been fitted with adaptive optics. Then they processed the
images with a special computer program, which Dr. Marois described as “a
software coronagraph,” for processing the images.
The team first spied a pair of dots about four billion and six billion miles out
from HR 8799 in October last year. Following up, they discovered a third planet
closer in, at about two billion miles. Then they discovered an old observation
from 2004, which also showed the planets and how far they had moved around the
star in three years.
“Seeing the orbit is one of the coolest things,” Dr. Macintosh said.
Dr. Kalas did his work with the Hubble Space Telescope, which is immune to
turbulence because it is in space. He used a coronagraph to block light from the
actual star.
He said he had been driven to look for a planet around Fomalhaut after Hubble
photographs in October 2004 showed that a dust ring around the star had a
suspiciously sharp inner edge, often a clue that the ring is being sculpted by
the gravity of some body orbiting nearby.
A second set of Hubble observations, in July 2006, revealed a dot moving
counterclockwise around the star. “I basically held my breath for three days
until I could confirm the existence of Fomalhaut in all of my data,” Dr. Kalas
recalled.
Fomalhaut is also a young star, about 200 million years old, and its dust ring
extends 11 billion to 20 billion miles from its planet, Dr. Kalas said. In order
not to disturb or roil the dust ring, Fomalhaut’s planet must be less than three
Jupiter masses, well within regulation planet size, Dr. Kalas and his
collaborators calculated.
A more detailed analysis, with another team member, Eugene Chiang of the
University of California, Berkeley, as lead author will appear in the
Astrophysical Journal, Dr. Kalas said.
In an e-mail message, Dr. Kalas pointed out that Fomalhaut was the closest
exoplanet yet discovered, “close enough to contemplate sending spacecraft
there.”
February
15, 2008
The New York Times
By DENNIS OVERBYE
Astronomers
said Wednesday that they had found a miniature version of our own solar system
5,000 light-years across the galaxy — the first planetary system that really
looks like our own, with outer giant planets and room for smaller inner planets.
“It looks like a scale model of our solar system,” said Scott Gaudi, an
assistant professor of astronomy at Ohio State University. Dr. Gaudi led an
international team of 69 professional and amateur astronomers who announced the
discovery in a news conference with reporters.
Their results are being published Friday in the journal Science. The discovery,
they said, means that our solar system may be more typical of planetary systems
across the universe than had been thought.
In the newly discovered system, a planet about two-thirds of the mass of Jupiter
and another about 90 percent of the mass of Saturn are orbiting a reddish star
at about half the distances that Jupiter and Saturn circle our own Sun. The star
is about half the mass of the Sun.
Neither of the two giant planets is a likely abode for life as we know it. But,
Dr. Gaudi said, warm rocky planets — suitable for life — could exist undetected
in the inner parts of the system.
“This could be a true solar system analogue,” he said.
Sara Seager, a theorist at the Massachusetts Institute of Technology who was not
part of the team, said that “right now in exoplanets we are on an inexorable
path to finding other Earths.” Dr. Seager praised the discovery as “a big step
in finding out if our planetary system is alone.”
Since 1995, around 250 planets outside the solar system, or exoplanets, have
been discovered. But few of them are in systems that even faintly resemble our
own. In many cases, giant Jupiter-like planets are whizzing around in orbits
smaller than that of Mercury. But are these typical of the universe?
Almost all of those planets were discovered by the so-called wobble method, in
which astronomers measure the gravitational tug of planets on their parent star
as they whir around it. This technique is most sensitive to massive planets
close to their stars.
The new discovery was made by a different technique that favors planets more
distant from their star. It is based on a trick of Einsteinian gravity called
microlensing. If, in the ceaseless shifting of the stars, two of them should
become almost perfectly aligned with Earth, the gravity of the nearer star can
bend and magnify the light from the more distant one, causing it to get much
brighter for a few days.
If the alignment is perfect, any big planets attending the nearer star will get
into the act, adding their own little boosts to the more distant starlight.
That is exactly what started happening on March 28, 2006, when a star 5,000
light-years away in the constellation Scorpius began to pass in front of one
21,000 light-years more distant, causing it to flash. That was picked up by the
Optical Gravitational Lensing Experiment, or Ogle, a worldwide collaboration of
observers who keep watch for such events.
Ogle in turn immediately issued a worldwide call for continuous observations of
what is now officially known as OGLE-2006-BLG-109. The next 10 days, as Andrew
P. Gould, a professor of mathematical and physical sciences at Ohio State said,
were “extremely frenetic.”
Among those who provided crucial data and appeared as lead authors of the paper
in Science were a pair of amateur astronomers from Auckland, New Zealand, Jennie
McCormick and Grant Christie, both members of a group called the Microlensing
Follow-Up Network, or MicroFUN.
Somewhat to the experimenters’ surprise, by clever manipulation they were able
to dig out of the data not just the masses of the interloper star and its two
planets, but also rough approximations of their orbits, confirming the
similarity to our own system. David P. Bennett, an assistant professor of
astrophysics at the University of Notre Dame, said, “This event has taught us
that we were able to learn more about these planets than we thought possible.”
As a result, microlensing is poised to become a major new tool in the planet
hunter’s arsenal, “a new flavor of the month,” Dr. Seager said.
Only six planets, including the new ones, have been discovered by microlensing
so far, and the Scorpius event being reported Friday is the first in which the
alignment of the stars was close enough for astronomers to detect more than one
planet at once. Their success at doing just that on their first try bodes well
for the future, astronomers say.
Alan Boss, a theorist at the Carnegie Institution of Washington, said, “The fact
that these are hard to detect by microlensing means there must be a good number
of them — solar system analogues are not rare.”
January 31, 2008
The New York Times
By WARREN E. LEARY
WASHINGTON — The Messenger spacecraft that zipped past Mercury two weeks ago
found more evidence of the innermost planet’s turbulent past, including ridges
that run hundreds of miles and a unique feature made up of more than 100 troughs
radiating in all directions, scientists said Wednesday.
A preliminary look at data from the flyby, including 1,213 images, shows a
small, cratered planet that superficially looks like Earth’s moon but is very
different in reality, they said.
The robot spacecraft, the first to visit the planet in more than three decades,
passed 124 miles above Mercury’s surface on Jan. 14 before continuing on a path
that is to bring it back three more times in the next three years before
settling into orbit.
During the encounter, the Messenger’s seven scientific instruments scanned the
planet, its magnetic field and its wispy atmosphere in great detail.
“Our little craft has returned a gold mine of exciting data,” said Dr. Sean C.
Solomon of the Carnegie Institution of Washington, the mission’s lead
investigator.
“We were continually surprised,” Dr. Solomon said at a NASA news conference. “It
was not the planet we expected. It was not the moon.”
Mercury remains a very dynamic planet and is a key to understanding the
evolution of the inner solar system and its four rocky planets, including Earth,
he said.
NASA’s Mariner 10 spacecraft, which made three flybys of Mercury in 1974 and
1975, mapped about 45 percent of the planet’s surface. The Messenger craft took
pictures of another 30 percent during its first visit and should complete the
portrait when it returns on its next flyby in October, scientists said.
After that visit and another in September 2009 to slow the craft, the Messenger
is to settle into orbit around Mercury on March 18, 2011, for at least a year of
studies.
Among the features spotted by the Messenger — short for the $446 million
mission’s formal name, Mercury Surface, Space Environment, Geochemistry and
Ranging — is one informally called “the spider.” It appears to be an impact
crater 25 miles in diameter from which more than 100 flat-bottomed troughs shoot
out in all directions, said Louise Prockter, an imaging instrument scientist at
the Johns Hopkins University Applied Physics Laboratory in Laurel, Md., which
built and operates the spacecraft.
“It’s a real mystery, a very unexpected find,” Ms. Prockter said, unlike
anything ever observed in the solar system. It is unclear if the impact crater
caused the shattered-looking feature or came later, after the troughs formed for
another reason, she said.
November 7, 2007
Filed at 10:53 p.m. ET
By THE ASSOCIATED PRESS
The New York Times
LOS ANGELES (AP) -- A new planet was discovered orbiting a
sun-like star 41 light years away, making it the first known planetary quintet
outside our solar system, astronomers said Tuesday.
The newfound planet joins four others circling the nearby star 55 Cancri in the
constellation Cancer. Although it resides in the star's so-called habitable
zone, a place where liquid water and mild temperatures should exist, it is more
like Saturn than Earth and therefore not likely to support life.
Still, scientists have not ruled out the possibility of finding an Earth-like
planet within the system as technology improves.
''It's a system that appears to be packed with planets,'' said co-discoverer
Debra Fischer, an astronomer at San Francisco State University.
Ranked fourth from 55 Cancri, the latest planet is about 45 times the mass of
Earth and has an orbit of 260 days. It was detected after nearly two decades of
observations by ground-based telescopes using the Doppler technique that
measures a planet's stellar wobble.
The other planets in the 55 Cancri system were discovered between 1996 and 2004.
The innermost planet is believed to resemble Neptune, while the most distant is
thought to be Jupiter-like.
Scientists have detected about 250 exoplanets, or planets orbiting a star other
than the sun. The 55 Cancri star holds the record for number of confirmed
planets. Only one other star is known to have four planets, while several others
have three or less.
''We can now say there are stars like the sun that have many worlds around
them,'' said planetary scientist Jonathan Lunine of the University of Arizona,
Tucson, who had no role in the discovery.
The research will appear in a future issue of the Astrophysical Journal. It was
funded by NASA, the National Science Foundation and the University of
California.
The latest discovery shows that our solar system is not unique, scientists said.
''When you look up into the night sky and see the twinkling lights of stars, you
can imagine with certainty that they have their own complement of planets,''
said astronomer Geoff Marcy of the University of California, Berkeley, who was
part
of the research.
August 4, 2006
The New York Times
By KENNETH CHANG
A tiny star with a giant planet is further
muddling astronomers’ notion of what a planet is. The planet is one of perhaps
only two or three planets around other stars to be photographed directly, but it
may be more like a star than a planet.
The tiny star, known as Oph1622, is so small that it never lighted up, a failed
star known as a brown dwarf. Even among brown dwarfs, it is small, with a mass
equal to 14 Jupiters, or about one-seventy-fifth that of the Sun.
In a paper published yesterday on the Web site of the journal Science,
astronomers at the University of Toronto and the European Southern Observatory
report that a photograph of Oph1622 also shows a planet about half as large as
the star itself, with a mass equal to seven Jupiters.
The two are separated by 22 billion miles, or about six times the distance
between the Sun and Pluto. Both are young, about a million years old.
Astronomers refer to them both by a recently coined word, planemo (pronounced
PLAN-uh-mo), short for planetary mass object — planet-size bodies that may or
may not be planets.
“It really stands out as something quite unusual and intriguing,” said Ray
Jayawardhana, a professor of astronomy at the University of Toronto and an
author of the Science paper. “The Oph1622 pair adds to the rich diversity of
worlds that have been discovered recently, a diversity that we couldn’t really
have imagined barely a decade ago.”
Within the solar system, astronomers have been debating where to put the
dividing line between planets and smaller clumps of rock and ice like comets and
asteroids. The discovery of an object larger than Pluto in the outer solar
system last year has rekindled debate on whether Pluto, by far the smallest
among the current roster of nine planets, should be demoted.
Outside the solar system, the dividing line between planets and stars has also
become blurry.
In the past decade astronomers have found 200 planets around other stars. Almost
all of these have been indirectly detected from a slight shift in the frequency
of a star’s light caused by the gravitational pull of a planet.
In 2004, astronomers reported the first direct sighting of a distant planet,
with about the mass of five Jupiters, seen next to a brown dwarf known as 2M1207
about 230 light-years away in the constellation Hydra. Astronomers have since
seen small, faint companions around a couple other stars, but are uncertain
whether those companions are planets or brown dwarfs.
Oph1622, about 400 light-years from Earth, should add to the confusion. Dr.
Jayawardhana said its companion had the mass of a planet but was born in the
manner of stars.
Star systems form in two steps. First, a cloud of gas collapses under gravity
into one, two and sometimes three stars. A disk of leftover gas and dust then
coalesces into planets.
But it is impossible to roll the clock back millions or billions of years, and
astronomers cannot conclusively say how some objects formed.
Brown dwarfs, by some definitions, have a mass greater than about 13 Jupiters,
the minimum amount for fusion reactions involving a heavy form of hydrogen known
as deuterium to begin. (The fusing of ordinary hydrogen requires much higher
temperatures and much higher mass, about 75 times that of Jupiter. That is the
upper mass limit for brown dwarfs.)
But some astronomers say that many brown dwarfs are embryonic stars that were
ejected out of nascent star systems. Others say that brown dwarfs formed just
like other stars, but from smaller gas clouds. Astronomers have also observed
free-floating planet-size objects not in orbit around a star, and they debate
whether these objects formed in the same way as stars or were ejected from other
star systems.
Astronomers had thought it was impossible to form stars much smaller than the
Sun, because the outward pressure of gas molecules bouncing around would keep
small gas clouds from collapsing. “People used to think it’s hard to make stars
this small,” said Paolo Padoan, a professor of physics at the University of
California, San Diego.
But Oph1622’s planet could not have formed the usual planet way, Dr.
Jayawardhana said. Most known planetary disks have only 1 percent to 2 percent
as much mass as the parent star, and thus the disk rotating around Oph1622 would
have been too small to produce a planet half as large as itself, he said.
Complex computer simulations by Dr. Padoan show that turbulence within the gas
clouds can generate shock waves traveling a few thousand miles per hour that
tear the clouds into smaller pieces and provide the necessary kick to overcome
the outward pressure and cause the smaller clouds to collapse.
