Astronomers said Thursday that they had found the most
Earth-like worlds yet known in the outer cosmos, a pair of planets that appear
capable of supporting life and that orbit a star 1,200 light-years from here, in
the northern constellation Lyra.
They are the two outermost of five worlds circling a yellowish star slightly
smaller and dimmer than our Sun, heretofore anonymous and now destined to be
known in the cosmic history books as Kepler 62, after NASA’s Kepler spacecraft,
which discovered them. These planets are roughly half again as large as Earth
and are presumably balls of rock, perhaps covered by oceans with humid, cloudy
skies, although that is at best a highly educated guess.
Nobody will probably ever know if anything lives on these planets, and the odds
are that humans will travel there only in their faster-than-light dreams, but
the news has sent astronomers into heavenly raptures. William Borucki of NASA’s
Ames Research Center, head of the Kepler project, described one of the new
worlds as the best site for Life Out There yet found in Kepler’s
four-years-and-counting search for other Earths. He treated his team to pizza
and beer on his own dime to celebrate the find (this being the age of
sequestration). “It’s a big deal,” he said.
Looming brightly in each other’s skies, the two planets circle their star at
distances of 37 million and 65 million miles, about as far apart as Mercury and
Venus in our solar system. Most significantly, their orbits place them both in
the “Goldilocks” zone of lukewarm temperatures suitable for liquid water, the
crucial ingredient for Life as We Know It.
Goldilocks would be so jealous.
Previous claims of Goldilocks planets with “just so” orbits snuggled up to red
dwarf stars much dimmer and cooler than the Sun have had uncertainties in the
size and mass and even the existence of these worlds, said David Charbonneau of
the Harvard-Smithsonian Center for Astrophysics, an exoplanet hunter and member
of the Kepler team.
“This is the first planet that ticks both boxes,” Dr. Charbonneau said, speaking
of the outermost planet, Kepler 62f. “It’s the right size and the right
temperature.” Kepler 62f is 40 percent bigger than Earth and smack in the middle
of the habitable zone, with a 267-day year. In an interview, Mr. Borucki called
it the best planet Kepler has found.
Its mate, known as Kepler 62e, is slightly larger — 60 percent bigger than Earth
— and has a 122-day orbit, placing it on the inner edge of the Goldilocks zone.
It is warmer but also probably habitable, astronomers said.
The Kepler 62 system resembles our own solar system, which also has two planets
in the habitable zone: Earth — and Mars, which once had water and would still be
habitable today if it were more massive and had been able to hang onto its
primordial atmosphere.
The Kepler 62 planets continue a string of breakthroughs in the last two decades
in which astronomers have gone from detecting the first known planets belonging
to other stars, or exoplanets, broiling globs of gas bigger than Jupiter, to
being able to discern smaller and smaller more moderate orbs — iceballs like
Neptune and, now, bodies only a few times the mass of Earth, known technically
as super-Earths. Size matters in planetary affairs because we can’t live under
the crushing pressure of gas clouds on a world like Jupiter. Life as We Know It
requires solid ground and liquid water — a gentle terrestrial environment, in
other words.
Kepler 62’s newfound worlds are not quite small enough to be considered strict
replicas of Earth, but the results have strengthened the already strong
conviction among astronomers that the galaxy is littered with billions of
Earth-size planets, perhaps as many as one per star, and that astronomers will
soon find Earth 2.0, as they call it — our lost twin bathing in the rays of an
alien sun.
“Kepler and other experiments are finding planets that remind us more and more
of home,” said Geoffrey Marcy, a longtime exoplanet hunter at the University of
California, Berkeley, and Kepler team member. “It’s an amazing moment in
science. We haven’t found Earth 2.0 yet, but we can taste it, smell it, right
there on our technological fingertips.”
A team of 60 authors, led by Mr. Borucki, reported the discovery of the Kepler
62 planets on Thursday in an article published online in the journal Science and
at a news conference at Ames.
As if that weren’t enough, a group led by Thomas Barclay of Ames and the Bay
Area Environmental Research Institute also reported the discovery of a planet
1.7 times as big as Earth hovering on the inner, warmer edge of the Goldilocks
zone of Kepler 69, a star almost identical to the Sun, 2,700 light-years
distant. At the news conference, Dr. Barclay described the planet as perhaps a
“Super-Venus.” The group’s paper was published on Thursday in The Astrophysical
Journal.
And in another paper submitted to The Astrophysical Journal, a group led by Lisa
Kaltenegger of the Harvard-Smithsonian Center for Astrophysics and the Max
Planck Institute for Astronomy, in Heidelberg, Germany, took the first stab at
trying to model conditions on the Kepler 62 planets. That is a tough job because
the system is too far away for astronomers to measure the masses of these
planets, which would allow the densities and compositions of the planets to be
pinned down, or to inspect and analyze their atmospheres with telescopes.
Scaling up from the properties of the Earth, Dr. Kaltenegger and her colleagues
concluded that both of them were probably ocean worlds with humid, cloudy skies.
Any life on them would probably be aquatic, she said, but “it might even be
cooler life than we have here. Looking at the oceans, we find a lot of
interesting life-forms there.”
Dr. Kaltenegger said she envisioned the pair as a kind of Darwinian test tube
and wondered in an e-mail if life would evolve on both worlds and, if so, “Would
life evolve ‘the same’ way or would there be very different life?”
“This is huge for the overall life-elsewhere question,” said Sara Seager, a
planetary expert at the Massachusetts Institute of Technology who was not part
of the work.
Alan Boss, a planetary expert at the Carnegie Institution of Washington and a
member of the Kepler team, called the new results the capstone of the Kepler
mission. “I would argue,” he said in an e-mail, “that if this was all that we
learned from Kepler, that the cost of this mission was justified.”
Kepler, launched in March 2009, hunts planets by staring at 150,000 stars in a
patch of Milky Way sky, monitoring their brightnesses and looking for blips
caused when planets pass in front of their home stars. To date the spacecraft
has identified 115 planets and has a list of 2,740 other candidates. (Over all,
the world’s astronomers now know of almost 1,000 exoplanets.)
But Kepler, which had its mission extended for four years last spring, is only
now coming into its prime. A minimum of three blips is required to register a
planet, and so planets like the Earth that take a year to make an orbit are only
now coming into view in the Kepler data. Indeed, the new Kepler 62 planets each
registered just three transits, as they are called.
But there is a hitch, Dr. Seager and others cautioned. Because the Kepler stars
are all so far away — hundreds or thousands of light-years — and the planets we
want to find are so small, astronomers will never be quite completely sure what
any particular planet is made of or whether anything can or does live there.
In the case of Kepler 62, said Natalie Batalha of San Jose State University, a
Kepler scientist, the astronomers had determined the composition of the new
planets by comparison to three earlier objects that had similar sizes and turned
out to be rocky.
“Mass by association,” Dr. Batalha called it in an e-mail.
Which is fine if all you want is the statistics of the cosmos. As Dr. Seager
pointed out, “Kepler was not designed to tell us which planet to go live on,
only how common Earth-like planets are.”
This article has been revised
to reflect the following
correction:
Correction: April 18, 2013
A headline on an earlier version of this article misstated
the distance of the newly discovered planets from
earth.
March 11, 2008
The New York Times
By DENNIS OVERBYE
In the end, there won’t even be fragments.
If nature is left to its own devices, about 7.59 billion years from now Earth
will be dragged from its orbit by an engorged red Sun and spiral to a rapid
vaporous death. That is the forecast according to new calculations by a pair of
astronomers, Klaus-Peter Schroeder of the University of Guanajuato in Mexico and
Robert Connon Smith of the University of Sussex in England.
Their report, to be published in the Monthly Notices of the Royal Astronomical
Society, is the latest and gloomiest installment yet in a long-running debate
about the ultimate fate of our planet. Only last year, the discovery of a giant
planet orbiting the faint burned-out cinder of a star in Pegasus had suggested
that Earth could survive the Sun’s death.
Dr. Smith called the new result “a touch depressing” in a series of e-mail
messages. But “looked at another way,” he added, “it is an incentive to do
something about finding ways to leave our planet and colonize other areas in the
galaxy.”
As for sentimental attachment to any of the geographic features we might have
come to know and love, Dr. Smith said, “I should add that the Himalayas are a
passing thought anyway. They didn’t even exist until India smashed into Asia
less than 60 million years ago — the blink of an eye compared with the billions
of years we are discussing.”
While he does not expect the argument to end, Dr. Smith said in an e-mail
message that, if anything, in the new calculations he and Dr. Schroeder had
underestimated the forces that would be dragging the Earth down toward the Sun.
“So,” he said, “I would be surprised if anyone were able to rescue the Earth
again in a future paper.”
Roberto Silviotti of the Capodimonte Observatory in Naples, Italy, who found the
planet around that dead star in Pegasus, said it was not surprising that people
were interested in the fate of the earth, adding, “I think that the point is not
only that this is our planet but also that the we know the solar system and the
Sun much better than any other planetary system and therefore we should be able,
potentially, to make much better forecasts.”
Earth’s basic problem is that the Sun will gradually get larger and more
luminous as it goes through life, according to widely held theories of stellar
evolution. In its first 4.5 billion years, according to the models, the Sun has
already grown about 40 percent brighter.
Over the coming eons, life on Earth will become muggier and more uncomfortable
and finally impossible.
“Even if the Earth were to marginally escape being engulfed,” said Mario Livio,
an astronomer at the Space Telescope Science Institute, “it would still be
scorched, and life on Earth would be destroyed.”
About a billion years from now, the Sun will be 10 percent brighter. Oceans on
Earth will boil away. The Sun will run out of hydrogen fuel in its core about
5.5 billion years from now and start burning hydrogen in the surrounding layers.
As a result, the core will shrink and the outer layers will rapidly expand as
the Sun transforms itself into a red giant.
The heat from this death rattle will transform the solar system; it will briefly
be springtime in the Kuiper Belt out beyond Neptune. Mercury and Venus will
surely be swallowed, but the Earth’s fate has always been more uncertain.
The reason is that in the course of ballooning outward, the Sun will blow off a
substantial share of its mass. Thus, the Sun’s gravitational grip on its planets
will be weakened, and they will retreat to more distant orbits. The Earth will
wind up about where Mars is now, “on the border line between being engulfed or
escaping engulfment,” as Dr. Livio put it.
Whether or not the Earth is engulfed depends on which of two effects wins out.
At the same time that the Earth is retreating to a safer position, tidal forces
between it and the expanding Sun will try to drag the planet inward and
downward. In 2001, an analysis of these opposing forces by Kacper Rybicki of the
Polish Institute of Geophysics and Carlos Denis of the University of Liege
concluded that it looked bad but that the Earth might have a chance of
surviving.
According to Dr. Smith and Dr. Schroeder, that chance is nil. One key to their
work is a new way of calculating how much mass the Sun loses during its
cataclysmic expansion, and, thus, how big it gets and how far the Earth
eventually moves outward. The more mass lost, paradoxically, the bigger the Sun
swells, like a balloon whose elastic weakens when it is stretched. Using a new
technique, developed by Dr. Schroeder and Manfred Cuntz of the University of
Texas in Arlington, the authors calculated that the lost mass would amount to a
third of the Sun’s original mass, compared with previous estimates of a quarter.
As a result, the red giant version of the Sun — at its maximum — will be 256
times as big across as the star is today and 2,730 times as luminous.
Skimming over the flame tops of this giant, the bare, burned Earth would produce
a bulge in the Sun. But friction would cause the bulge to lag as it tried to
follow the Earth. The gravitational tug from the bulge would slow the Earth and
would cause it to spiral inward, where friction from gases in the Sun’s expanded
atmosphere would slow it even more.
Then it would go down.
After a period of burning helium and shrinking and expanding and then finally
shrinking again, the Sun will wind up as tiny cinder known as a white dwarf,
fading away for the rest of time.
Is there any way out of this fiery end for the robots or cockroaches or whoever
will be running the Earth in a billion years?
One option is to leave for another planet or another star system.
Another option, Dr. Smith said, is to engage in some large-scale high-stakes
engineering.
In the same way that space probes can get a trajectory boost by playing
gravitational billiards with Venus or Jupiter to gain speed and get farther out
in space, so the Earth could engineer regular encounters with a comet or
asteroid, thus raising its orbit and getting farther from the Sun, according to
a paper in 2001 by Don Korycansky and Gregory Laughlin of the University of
California, Santa Cruz, and Fred Adams of the University of Michigan.
Dr. Laughlin said that when their paper first came out, they were praised by the
radio host Rush Limbaugh and other conservatives for forward thinking.
But Dr. Laughlin said they were actually not advocating the orbit-shifting
project, noting that a miscalculation could lead to the comet’s hitting the
Earth.
“There are profound ethical issues involved,” he wrote in an e-mail message,
“and the cost of failure (an Earth-sterilizing impact) is unacceptably high.”
Anyway, such a maneuver would prolong the viability of the Earth for only a few
billion years. After that, the planet would be stranded in the cold and dim.
Stephen Hawking warned that future generations
would need to leave the planet to ensure the survival of the species as he
picked up a prestigious scientific accolade yesterday.
Professor Hawking, 64, a mathematics professor at the University of Cambridge,
said space rockets using the kind of technology seen in Star Trek would be
needed to colonise hospitable planets.
His warning came as he collected Britain's highest scientific award, the Royal
Society's Copley Medal, previously granted to Charles Darwin, Michael Faraday
and Captain James Cook. Professor Hawking, who suffers from motor neurone
disease, said he was "honoured" to be in the company of such esteemed men.
The society's president, Lord Rees, said he had contributed "as much as anyone
since Einstein to our understanding of gravity".
Professor Hawking also spoke of his desire to go into space, and appealed to the
Virgin tycoon, Sir Richard Branson, who is planning a "space tourism" venture,
to realise his ambition. "My next goal is to go into space. Maybe Richard
Branson will help me," he said.
In an interview with BBC Radio 4, he said scientists may be within 20 years of
reaching the prediction in his book, A Brief History of Time, that mankind would
one day "know the mind of God" by understanding the laws governing the universe.
He added that this knowledge may be vital to the human race's continued
existence. "The long-term survival of the human race is at risk as long as it is
confined to a single planet.
"Sooner or later, disasters such as an asteroid collision or nuclear war could
wipe us all out. But once we spread out into space and establish independent
colonies, our future should be safe. There isn't anywhere like the Earth in the
solar system, so we would have to go to another star.
"If we used chemical fuel rockets like the Apollo mission to the moon, the
journey to the nearest star would take 50,000 years. This is obviously far too
long to be practical, so science fiction has developed the idea of warp drive,
which takes you instantly to your destination. Unfortunately, this would violate
the scientific law which says that nothing can travel faster than light.
"However, we can still within the law, by using matter/antimatter annihilation,
at least reach just below the speed of light. With that, it would be possible to
reach the next star in about six years, though it wouldn't seem so long for
those on board," he said.
The cult science-fiction series, Star Trek, has featured matter/antimatter
annihilation as an explanation for the warp drive which powers spaceships like
the Enterprise through vast distances in short periods.
But in reality, some scientists believe the radiation produced when matter and
antimatter are brought together could one day be used to accelerate aircrafts
close to the speed of light.
Meanwhile, to recognise Professor Hawking's achievements, the British astronaut
Piers Sellers carried his medal into space on the July shuttle mission.
"Stephen Hawking is a hero to all of us involved in exploring the cosmos. It was
an honour for the crew of the STS-121 mission to fly his medal into space," he
said.
