A Neptune-size planet with a clear atmosphere is
shown crossing in front of its star in this artist's depiction. Such crossings,
or transits, are observed by telescopes like NASA's Hubble and Spitzer to glean
information about planets' atmospheres.
Image Credit:
NASA/JPL-Caltech
Feature Link:
Scientists were excited to discover clear skies on
a relatively small planet, about the size of Neptune, using the combined power
of NASA's Hubble, Spitzer and Kepler space telescopes.
Feature Link:
A plot of the transmission spectrum for exoplanet
HAT-P-11b, with data from NASA's Kepler, Hubble and Spitzer observatories
combined. The results show a robust detection of water absorption in the Hubble
data. Transmission spectra of selected atmospheric models are plotted for
comparison.
Image Credit:
NASA/ESA/STScI
Astronomers using data from three of NASA's space telescopes -- Hubble,
Spitzer and Kepler -- have discovered clear skies and steamy water vapor on a
gaseous planet outside our solar system. The planet is about the size of
Neptune, making it the smallest planet from which molecules of any kind have
been detected.
“This discovery is a significant milepost on the road to eventually analyzing
the atmospheric composition of smaller, rocky planets more like Earth,” said
John Grunsfeld, assistant administrator of NASA’s Science Mission Directorate in
Washington. “Such achievements are only possible today with the combined
capabilities of these unique and powerful observatories.”
Clouds in a planet’s atmosphere can block the view to underlying molecules
that reveal information about the planet’s composition and history. Finding
clear skies on a Neptune-size planet is a good sign that smaller planets might
have similarly good visibility.
"When astronomers go observing at night with telescopes, they say 'clear
skies' to mean good luck," said Jonathan Fraine of the University of Maryland,
College Park, lead author of a new study appearing in Nature. "In this case, we
found clear skies on a distant planet. That's lucky for us because it means
clouds didn't block our view of water molecules."
The planet, HAT-P-11b, is categorized as an exo-Neptune -- a Neptune-sized
planet that orbits the star HAT-P-11. It is located 120 light-years away in the
constellation Cygnus. This planet orbits closer to its star than does our
Neptune, making one lap roughly every five days. It is a warm world thought to
have a rocky core and gaseous atmosphere. Not much else was known about the
composition of the planet, or other exo-Neptunes like it, until now.
Part of the challenge in analyzing the atmospheres of planets like this is
their size. Larger Jupiter-like planets are easier to see because of their
impressive girth and relatively inflated atmospheres. In fact, researchers
already have detected water vapor in the atmospheres of those planets. The
handful of smaller planets observed previously had proved more difficult to
probe partially because they all appeared to be cloudy.
In the new study, astronomers set out to look at the atmosphere of HAT-P-11b,
not knowing if its weather would call for clouds. They used Hubble's Wide Field
Camera 3, and a technique called transmission spectroscopy, in which a planet is
observed as it crosses in front of its parent star. Starlight filters through
the rim of the planet's atmosphere; if molecules like water vapor are present,
they absorb some of the starlight, leaving distinct signatures in the light that
reaches our telescopes.
Using this strategy, Hubble was able to detect water vapor in HAT-P-11b. But
before the team could celebrate clear skies on the exo-Neptune, they had to show
that starspots -- cooler "freckles" on the face of stars -- were not the real
sources of water vapor. Cool starspots on the parent star can contain water
vapor that might erroneously appear to be from the planet.
The team turned to Kepler and Spitzer. Kepler had been observing one patch of
sky for years, and HAT-P-11b happens to lie in the field. Those visible-light
data were combined with targeted Spitzer observations taken at infrared
wavelengths. By comparing these observations, the astronomers figured out that
the starspots were too hot to have any steam. It was at that point the team
could celebrate detecting water vapor on a world unlike any in our solar system.
This discovery indicates the planet did not have clouds blocking the view, a
hopeful sign that more cloudless planets can be located and analyzed in the
future.
"We think that exo-Neptunes may have diverse compositions, which reflect
their formation histories," said study co-author Heather Knutson of the
California Institute of Technology in Pasadena. "Now with data like these, we
can begin to piece together a narrative for the origin of these distant
worlds."
The results from all three telescopes demonstrate that HAT-P-11b is blanketed
in water vapor, hydrogen gas and likely other yet-to-be-identified molecules.
Theorists will be drawing up new models to explain the planet's makeup and
origins.
"We are working our way down the line, from hot Jupiters to exo-Neptunes,"
said Drake Deming, a co-author of the study also from University of Maryland.
"We want to expand our knowledge to a diverse range of exoplanets."
The astronomers plan to examine more exo-Neptunes in the future, and hope to
apply the same method to super-Earths -- massive, rocky cousins to our home
world with up to 10 times the mass. Although our solar system doesn't have a
super-Earth, NASA's Kepler mission is finding them in droves around other stars.
NASA's James Webb Space Telescope, scheduled to launch in 2018, will search
super-Earths for signs of water vapor and other molecules; however, finding
signs of oceans and potentially habitable worlds is likely a ways off.
"The work we are doing now is important for future studies of super-Earths
and even smaller planets, because we want to be able to pick out in advance the
planets with clear atmospheres that will let us detect molecules," said
Knutson.
Once again, astronomers will be crossing their fingers for clear skies.
More information about Hubble, Kepler and Spitzer is online at:
http://www.nasa.gov
Mission Manager Update: C1 data on the ground; C2
underway
The K2 mission has successfully completed its first official set of science
observations and the data are on the ground! Campaign 2 observations are now
underway.
The team is processing and preparing the data from
Campaign
1, which are scheduled to be delivered to the public at the
Mikulski Archive for Space Telescopes
(MAST) in November. Campaign 1 targets included more than 12,000 stars for
exoplanet transit searches, as well as young and old star clusters and galaxies.
The latter are being examined for black hole accretion activity or
supernovae.
The image is a mosaic of "postage stamp" regions
taken during the engineering test run this spring by NASA's Kepler spacecraft
operating in the two-wheel K2 mode. Highlighted in the image are two open
clusters Messier 35 (top) and NGC 2158 (bottom).
Image Credit:
NASA Ames/T Barclay/W Stenzel
This past spring the team performed an end-to-end shakedown of spacecraft
operations and performance in the new two-wheel K2 mode. While this was
primarily an engineering test, science observations were made on approximately
8,000 targets, including the open star cluster Messier 35 and the compact open
star cluster NGC 2158, both in the constellation Gemini. Coined "Campaign 0,"
these data were delivered to the public
archive
at MAST on Monday, Sept. 8.
The team is now accepting target proposals for Campaigns 4 and 5. The
deadline for
K2
Cycle-1 Stage-2 Guest Observer proposals is 23:59 p.m. EDT on Sept. 23. For
the full schedule of operational milestones see the K2 Mission
Timeline.
On Aug. 23, the K2 mission began its second campaign. The Campaign 2 field of
view includes the globular star clusters M4 and M80 in the constellation of
Scorpius, the very dense star-forming region Rho Ophiuchi, along with 17,000
target stars that can be searched for exoplanets. In mid-October, Comet Siding
Spring will be observed for approximately 77 hours as it passes through Kepler's
field of view. Many other NASA missions also will be pointed toward the comet.
Mars also passes through the field of view, but is too bright to be observed.
The campaign is scheduled to conclude on Nov. 11, and will be our first K2
campaign to go from start to finish without a break in the middle.
Meanwhile, the spacecraft continues to deliver robust performance in its
two-wheel K2 mode. In early August, a reassessment of the fuel usage increased
the expected life of the spacecraft by 25 percent. At the current burn rate, the
onboard fuel reserves are now expected to last until late 2017, and perhaps
beyond. And last week the spacecraft weathered the effects of a large solar
flare
without missing a beat!
To learn more about the K2 mission visit the Kepler Science Center
website.
Despite ongoing K2 operations, the bulk of the mission science focus remains
on finalizing the data processing and products for the formal Kepler mission.
Two more releases of the data processing pipeline are scheduled that will
include enhancements to increase the sensitivity to small planets in long-period
orbits, similar to Earth, and determine their frequency in the galaxy-- Kepler's
primary objective.
The following are highlights of recent research using Kepler data that have
been accepted by a peer-review journal:
- Most Sub-Arcsecond Companions of
Kepler Exoplanet Candidate Host Stars are Gravitationally Bound (Horch et
al., 2014) – This paper finds that about half of the stars hosting planets are
actually binary stars. That is, a pair of stars where the planet orbits one of
the stars while the other is a bright nighttime spectacle.
- The Variable Sky of Deep Synoptic
Surveys (Ridgway et al., 2014) - Using Kepler light curves to understand how
stars and galaxies vary, this paper extends these results to the entire sky to
estimate the science yield that will come from the Large Synoptic Survey
Telescope and the Gaia space mission, both to undertake all-sky surveys within
the next decade.
- On the Frequency of Potential Venus
Analogs from Kepler Data (Kane et al., 2014) – The sensitivity of Kepler
data to Earth-sized planets allows us to investigate the frequency of Venus
analogs since these planets are similar in size; however, Venus has a runaway
greenhouse atmosphere. By using climate models to calculate the distances from a
star where a runaway greenhouse would occur, this paper defines a "Venus Zone"
for potential Venus analogs and estimates that almost half of sun-like stars
harbor an analog to our sister planet.
For the latest Kepler exoplanet and candidate statistics, visit the
NASA Exoplanet
Archive. The Kepler light curves are available at
MAST.
