NASA’s Kepler space telescope team has released a mission catalog of planet candidates that introduces 219 new planet candidates, 10 of which are near-Earth size and orbiting in their star's habitable zone, which is the range of distance from a star where liquid water could pool on the surface of a rocky planet.
This is the most comprehensive and detailed catalog release of
candidate exoplanets, which are planets outside our solar system, from
Kepler’s first four years of data. It’s also the final catalog from the
spacecraft’s view of the patch of sky in the Cygnus constellation.
With the release of this catalog, derived from data publicly available on the NASA Exoplanet Archive,
there are now 4,034 planet candidates identified by Kepler. Of which,
2,335 have been verified as exoplanets. Of roughly 50 near-Earth size
habitable zone candidates detected by Kepler, more than 30 have been
verified.
Additionally, results using Kepler data suggest two distinct size
groupings of small planets. Both results have significant implications
for the search for life. The final Kepler catalog will serve as the
foundation for more study to determine the prevalence and demographics
of planets in the galaxy, while the discovery of the two distinct
planetary populations shows that about half the planets we know of in
the galaxy either have no surface, or lie beneath a deep, crushing
atmosphere – an environment unlikely to host life.
The findings were presented at a news conference Monday at NASA's Ames Research Center in California's Silicon Valley.
“The Kepler data set is unique, as it is the only one containing a
population of these near Earth-analogs – planets with roughly the same
size and orbit as Earth,” said Mario Perez, Kepler program scientist in
the Astrophysics Division of NASA’s Science Mission Directorate.
“Understanding their frequency in the galaxy will help inform the design
of future NASA missions to directly image another Earth.”
The Kepler space telescope hunts for planets by detecting the
minuscule drop in a star’s brightness that occurs when a planet crosses
in front of it, called a transit.
This is the eighth release of the Kepler candidate catalog, gathered
by reprocessing the entire set of data from Kepler’s observations during
the first four years of its primary mission. This data will enable
scientists to determine what planetary populations – from rocky bodies
the size of Earth, to gas giants the size of Jupiter – make up the
galaxy’s planetary demographics.
To ensure a lot of planets weren't missed, the team introduced their
own simulated planet transit signals into the data set and determined
how many were correctly identified as planets. Then, they added data
that appear to come from a planet, but were actually false signals, and
checked how often the analysis mistook these for planet candidates. This
work told them which types of planets were overcounted and which were
undercounted by the Kepler team’s data processing methods.
“This carefully-measured catalog is the foundation for directly
answering one of astronomy’s most compelling questions – how many
planets like our Earth are in the galaxy?” said Susan Thompson, Kepler
research scientist for the SETI Institute in Mountain View, California,
and lead author of the catalog study.
One research group took advantage of the Kepler data to make precise
measurements of thousands of planets, revealing two distinct groups of
small planets. The team found a clean division in the sizes of rocky,
Earth-size planets and gaseous planets smaller than Neptune. Few planets
were found between those groupings.
Using the W. M. Keck Observatory in Hawaii, the group measured the
sizes of 1,300 stars in the Kepler field of view to determine the radii
of 2,000 Kepler planets with exquisite precision.
“We like to think of this study as classifying planets in the same way that biologists identify new species of animals,” said Benjamin Fulton, doctoral candidate at the University of Hawaii in Manoa, and lead author of the second study. “Finding two distinct groups of exoplanets is like discovering mammals and lizards make up distinct branches of a family tree.”
It seems that nature commonly makes rocky planets up to about 75
percent bigger than Earth. For reasons scientists don't yet understand,
about half of those planets take on a small amount of hydrogen and
helium that dramatically swells their size, allowing them to "jump the
gap" and join the population closer to Neptune’s size.
The Kepler spacecraft continues to make observations in new patches
of sky in its extended mission, searching for planets and studying a
variety of interesting astronomical objects, from distant star clusters
to objects such as the TRAPPIST-1 system of seven Earth-size planets, closer to home.
Ames manages the Kepler missions for NASA’s Science Mission
Directorate. NASA's Jet Propulsion Laboratory in Pasadena, California,
managed Kepler mission development. Ball Aerospace & Technologies
Corporation operates the flight system with support from the Laboratory
for Atmospheric and Space Physics at the University of Colorado in
Boulder.
For more information about the Kepler mission, visit: https://www.nasa.gov/kepler
Felicia Chou
Headquarters, Washington
202-358-0257
felicia.chou@nasa.gov
Michele Johnson
Ames Research Center, California’s Silicon Valley
650-604-6882
michele.johnson@nasa.gov
Elizabeth Landau
Jet Propulsion Laboratory, Pasadena, Calif.
818-354-6425
elizabeth.landau@jpl.nasa.gov
Editor: Karen Northon
Source: NASA/Kepler and K2
