This
whimsical cartoon shows the three newly discovered extrasolar planets
(right) casting shadows on their host star that can been seen as
eclipses, or transits, at Earth (left). Earth can be detected by the
same effect, but only in the plane of Earth's orbit (the ecliptic).
During the K2 mission, many of the extrasolar planets discovered by the
Kepler telescope will have this lucky double cosmic alignment that would
allow for mutual discovery—if there is anyone on those planets to
discover Earth. The three new planets orbiting EPIC 201367065 are just
out of alignment; while they are visible from Earth, our solar system is
tilted just out of their view. Credit: K. Teramura, UH IfA. High-resolution version
MAUNA KEA, HI – A team of scientists recently discovered a system of three planets, each just
larger than Earth, orbiting a nearby star called EPIC 201367065. The three
planets are 1.5-2 times the size of Earth.
The outermost planet orbits on the
edge of the so-called “habitable zone,” where the temperature may be just right
for liquid water, believed necessary to support life, on the planet’s
surface. The paper, “A Nearby M Star with Three Transiting Super-Earths Discovered
by K2,” was submitted to the Astrophysical Journal today and is available here.
“The
compositions of these newfound planets are unknown, but, there is a very real
possibility the outer planet is rocky like Earth,” said Erik Petigura, a
University of California, Berkeley graduate student who spent a year visiting
the UH Institute for Astronomy. “If so, this planet could have the right
temperature to support liquid water oceans.”
The
planets were confirmed by the NASA Infrared Telescope Facility (IRTF) and the W. M.
Keck Observatory in Hawaii as well as telescopes in California and Chile.
“Keck's contribution to this discovery was vital,” said
Andrew Howard, a University of Hawaii astronomer on the team.
“The adaptive optics image from NIRC2 showed the star hosting these three
planets is a single star, not a binary. It showed that the planets are real and
not an artifact of some masquerading multi-star system.”
Due to the competitive state of planet finding, and
the fact that time on the twin Keck telescopes are scheduled months in advance,
the team asked UC Berkeley Astronomer, Imke de Pater to gather some data during
her scheduled run.
“The collegiality of the Keck Observatory community
is just wonderful,” Howard said. “Imke took time away from her own science
observations to get us images of this system, all on a couple hours’ notice.”
The
new discovery paves the way for studies of the atmosphere of a warm planet
nearly the size of Earth.
“We’ve
learned in the past year that planets the size and temperature of Earth are
common in our Milky Way galaxy,” Howard said. “We also discovered some
Earth-size planets that appear to be made of the same materials as our Earth,
mostly rock and iron.”
The
astronomers next hope to determine what elements are in the planets’
atmospheres. If these warm, nearly Earth-size planets have thick, hydrogen-rich
atmospheres, there is not much chance for life.
“A
thin atmosphere made of nitrogen and oxygen has allowed life to thrive on
Earth. But nature is full of surprises. Many extrasolar planets discovered by
the Kepler Mission are enveloped by thick, hydrogen-rich atmospheres that are
probably incompatible with life as we know it,” said Ian Crossfield, the
University of Arizona astronomer who led the study.
The
discovery is all the more remarkable because Kepler is now hobbled by the loss
of two reaction wheels that kept it pointing at a fixed spot in space. Kepler,
launched in 2009, was reborn in 2014 as “K2” with a clever strategy of pointing
the telescope in the plane of the Earth’s orbit to stabilize the spacecraft.
Kepler is back to mining the cosmos for planets by searching for eclipses, or
transits, as planets orbit in front of their host stars and periodically block
some of the starlight.
“I
was devastated when Kepler was crippled by a hardware failure,” Petigura added.
“It’s a testament to the ingenuity of NASA engineers and scientists that Kepler
can still do great science.”
Kepler
sees only a small fraction of the planetary systems in its gaze, those with
orbital planes aligned edge-on to our view from Earth. Planets with large
orbital tilts are simply missed by Kepler.
“It’s
remarkable that the Kepler telescope is now pointed in the ecliptic, the plane
that Earth sweeps out as it orbits the Sun,” Fulton explains. “This means that
some of the planets discovered by K2 will have orbits lined up with Earth’s, a
celestial coincidence that allows Kepler to see the alien planets, and
Kepler-like telescopes in those very planetary systems (if there are any) to
discover Earth.”
“Here’s
looking at you, looking at me,” said Howard.
In
addition to Howard and Petigura, UH graduate students Benjamin Fulton and
Kimberly Aller, and UH astronomer Michael Liu were among the two dozen
scientists who contributed to the study.
The W. M. Keck Observatory operates the
largest, most scientifically productive telescopes on Earth. The two, 10-meter
optical/infrared telescopes near 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 spectrographs and
world-leading laser guide star adaptive optics systems.
NIRC2 (the
Near-Infrared Camera, second generation) works in combination with the Keck II
adaptive optics system to obtain very sharp images at near-infrared
wavelengths, achieving spatial resolutions comparable to or better than those
achieved by the Hubble Space Telescope at optical wavelengths. NIRC2 is
probably best known for helping to provide definitive proof of a central
massive black hole at the center of our galaxy. Astronomers also use NIRC2 to
map surface features of solar system bodies, detect planets orbiting other
stars, and study detailed morphology of distant galaxies.
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.
Steve Jefferson
Communications Officer
W. M. Keck Observatory
808.881.3827
sjefferson@keck.hawaii.edu
Source: W. M. Keck Observatory
