Download Time runs out for Herschel

News • Mission Update
Space Shorts
After Kepler, TESS
NASA’s Astrophysics Explorer
Program has selected the
Transiting Exoplanet Survey
Satellite (TESS) mission to fly
in 2017. TESS will use an array
of four telescopes to perform
an all-sky survey to discover
transiting exoplanets of all sizes
in orbit around the nearest and
brightest stars in the sky. Its goal
is to identify terrestrial planets
in the habitable zones of nearby
stars that are best suited for
extensive follow-up observations
and characterization, including
with the James Webb Space
Telescope. TESS will collect 10
times as much data during its
two-year mission as Kepler did
during its first two years. Its
principal investigator is George
Ricker of the Massachusetts
Institute of Technology.
http://1.usa.gov/12UIonD
NICER gets go-ahead
The Neutron Star Interior
Composition Explorer has
been chosen as the second
mission for NASA’s Astrophysics
Explorer Program. NICER will
be placed on the International
Space Station and will measure
the variability of cosmic X-ray
sources, a process called X-ray
timing, to explore the exotic
states of matter within neutron
stars and reveal their interior
and surface compositions. The
principal investigator is Keith
Gendreau of NASA’s Goddard
Space Flight Center.
http://heasarc.gsfc.nasa.gov/docs/nicer
Brightest, longest GRB
The highest-energy light ever
recorded from a gamma-ray
burst was detected by NASA’s
Fermi Gamma Ray Space
Telescope on 27 April and
then by automatically alerted
space-based observatories such
as Swift. Fermi’s Large Area
Telescope recorded a gammaray with an energy of at least
94 GeV and high-energy emission
from the burst was detectable
for most of a day rather than the
usual minutes. It was later seen
in optical, infrared and radio
wavelengths by ground-based
observatories, based on the
position from Swift. This burst
was about 3.6 billion light-years
away, in the nearest 5% of GRBs,
and astronomers then looked
for the supernova expected to be
found within a week or so.
http://1.usa.gov/10q2ie7
3.8
Mission update
Time runs out for Herschel
ESA’s Herschel space observatory
stopped working on 29 April after
more than three years of operation, when it exhausted its liquid
helium coolant. Herschel used the
biggest single mirror – 3.5 m diameter – built for a space observatory
and observed from far infrared to
submillimetre wavelengths. The
liquid helium was needed to cool
the instrument close to absolute
zero; rising instrument temperatures confirmed the end of this
phase of the mission.
Herschel’s science return is by no
means finished, however, as there
is plenty to discover within the legacy data. Herschel made more than
35 000 scientific observations,
amassing more than 25 000 hours’
worth of science data from about
600 observing programmes. A
further 2000 hours of calibration
observations also contribute to
the rich dataset, which is based at
ESA’s European Space Astronomy
Centre, near Madrid in Spain.
Herschel observes the cool, dark
universe, and has been a very
effective probe of water and other
volatiles in star-forming regions
and planetary discs, for example.
Now Herschel data have shown a
difference in stratospheric water
content between the northern and
southern hemispheres of Jupiter,
attributed to the impact of comet
Shoemaker-Levy 9 in July 1994.
Water was detected at the time
of the impact of comet SL9, but
direct proof of its persistence at
Jupiter was lacking. ESA’s Infrared
Space Observatory found water in
the stratosphere in 1997, and its
origin became a matter of debate;
there is not enough oxygen in the
upper atmospheric layers to form
Argon argues
for atmosphere
loss on Mars
Isotopes of noble gas argon provide
strong support for the idea that Mars
has lost much of its atmosphere over
time. Measurements of the martian
atmosphere using the quadrupole
mass spectrometer in the Sample
Analysis at Mars instrument (SAM)
on Mars Science Laboratory’s Curi-
1: Jupiter’s asymmetrical high-altitude water abundance in pale blue.
(ESA/Herschel/T Cavalié et al.; and NASA/ESA/R Beebe NMSU)
it there. Other possible sources
include local sources on the planet
or from rings and satellites of Jupiter or from interplanetary dust.
Now an international team led
by Thibault Cavalié of the University of Bordeaux/CNRS used the
Heterodyne Instrument for the Far
Infrared (HIFI) and the Photodetector Array Camera and Spectrometer (PACS) onboard Herschel
to map the distribution of water,
mapping Jupiter’s stratospheric
temperature with the NASA Infrared Telescope Facility (IRTF) at
the same time in order to measure
temperature independently. They
have produced a map of the disc of
Jupiter using PACS and a vertical
http://bit.ly/10qop41
osity rover found about four times as
much 36Ar as 38Ar. This ratio of stable
isotopes is significantly lower than
that in the solar system as a whole,
based on measurements from the Sun
and Jupiter, and points to a mechanism that preferentially removes
the lighter isotope rather than the
heavier one. Loss of atmospheric
constituents to space could produce
the stable isotope ratios observed.
Curiosity’s measurements are more
precise than previous estimates taken
from the Viking probe in 1976 and
from martian meteorites. Erosion
of the martian atmosphere by the
charged particles of the solar wind
was measured in 2004 by the European team using ASPERA-3 on ESA’s
Mars Express orbiter.
Curiosity’s SAM instrument suite
has also picked out volatile compounds in a sample of rocks drilled
at the Yellowknife site within Gale
Crater. The gases given off when
the powder sample was heated –
and the temperatures at which they
were detected – point towards rocks
profile through the stratosphere
using HIFI (figure 1). The water
is present at low pressures, in the
upper parts of the atmosphere, and
is more abundant in the southern
hemisphere than the northern. The
vertical profile indicates supply
from off the planet, relatively
recently so that it has not had time
to mix throughout Jupiter’s layers
and remove the asymmetry. While
moons, rings and interplanetary
dust cannot be entirely ruled out,
the majority of the water it likely
to have come from the comet
impact 19 years ago.
Cavalié et al. published the results
in Astronomy & Astrophysics.
A&G • June 2013 • Vol. 54
News • Mission Update
Cassini sees hurricane in Saturn’s hexagon
The Cassini spacecraft has taken
a close look at a vast storm system
within the hexagonal weather pattern
at the north pole of Saturn. The storm
looks very like a hurricane on Earth,
but it is much bigger: the clear central
eye of the storm is about 2000 km
across – ten times the typical size on
Earth – and clouds at the outer edge
of the hurricane on Saturn are moving
at more than 500 kph – rather faster
than on Earth! One difference from
terrestrial hurricanes is that this storm
is locked into the weather system at the
pole, rather than sweeping round the
planet as happens on Earth.
The existence of this storm poses
questions about both Saturn and
Earth. Terrestrial hurricanes get their
energy from warm ocean water; this
system on Saturn does not have a
handy warm ocean, although it does
use a relatively small amount of water
vapour within the hydrogen atmosphere. Understanding how this storm
system evolves may shed light on the
mechanisms of terrestrial storms.
Cassini is a joint project of NASA,
ESA and the Italian Space Agency and
has been observing Saturn since 2004.
Scientists have not seen the north pole
so clearly in the past because it is only
now emerging from winter. Cassini’s
composite infrared spectrometer and
visual and infrared mapping spectrometer detected the great hexagonal
vortex, but now it is visible. Cassini is
also getting better views of the poles
because it is following more highly
inclined orbits, using Titan’s gravity to
change the angle.
http://1.usa.gov/13yrn5x
containing hydrated minerals, carbonates, perchlorates, sulphates and
sulphides and clays. This was the
result of the fourth powder sample
from one rock (called John Klein by
the rover team) and highlights the
effectiveness of the powder analysis
that Curiosity can perform.
http://ssed.gsfc.nasa.gov/sam
Super-Earths
found around a
Sun-like star
NASA’s Kepler mission has found a
system of five small planets including
two “super-Earths” orbiting in the
habitable zone of the star, a K-type
star slightly smaller than the Sun.
If these planets are rocky or water
worlds, they are potential targets for
the search for extraterrestrial intelligence.
Kepler astronomers established
that this system comprises five planA&G • June 2013 • Vol. 54 2: A false-colour image of the north polar region of Saturn using filters sensitive to near-infrared light:
wavelengths of 890 nm are projected as blue, 728 nm as green, and 752 nm as red. Red indicates low clouds
and green indicates high ones. The image was taken from a distance of 419 000 km. (NASA/JPL-Caltech/SSI)
ets the size of Earth or a bit bigger
on the basis of repeated transit data,
reinforced by comparison with other
Kepler multiple-planet systems. The
outermost planet, Kepler-62f, about
1.4 times the radius of Earth with
a period of 267 Earth days, orbits
in the habitable zone for a planet
with an atmosphere like that of
Earth. Kepler-62e, about 1.6 times
Earth’s radius and with a period of
122 Earth days, is probably also in
the habitable zone so liquid water
may exist on its surface, too. But
because the Kepler team has only
transit data, the masses of these
planets remain uncertain and it is
not clear whether they are rocky or
perhaps water planets. They are also,
at 850 light-years distance, too far
from Earth for any atmospheric compositions to be determined.
This system is an especially significant discovery, however, because it
adds to the numbers of known systems including small planets that
orbit in their star’s habitable zones.
Knowing the distribution of such
small planetary systems will help
plan further research on them and
their characteristics, possibly including those closer to Earth.
http://www.seti.org/seti_kepler_62
HARPS-N gives
exoplanet mass
Astronomers have combined data
from the Kepler space telescope with
that from the new HARPS-N spectrograph on La Palma to characterize two new exoplanets, adding their
mass to determinations of planetary
radius and orbital period.
HARPS-N is the new high-accuracy spectrograph working in the
northern hemisphere, a counterpart to the HARPS instrument at
the European Southern Observatory, able to pick out radial velocity
variations of less than 1 m s –1. These
data complement Kepler’s transit
data, as established by work com-
bining high-resolution spectroscopy
from SOPHIE, an instrument at the
Observatoire de Haute-Provence
that has been examining exoplanets
since 2010.
An international team led by G
Hébrard (Institut d’Astrophysique
de Paris/Observatoire de HauteProvence) has now characterized two
Jupiter-sized planets with eccentric
orbits smaller than that of Mercury
in the solar system, and periods
of less than 10 days. KOI-200b is
slightly bigger and less massive than
Jupiter, orbiting around its star in
less than one week. The planet KOI889b is of the size of Jupiter but is
10 times more massive, orbiting
around its star in slightly less than 9
days. These two planets have eccentric orbits giving rise to variations
in their equilibrium temperature of
several hundred degrees over just a
few days. Such eccentric orbits are
rare for “hot Jupiters”, giant planets
orbiting close to their parent stars.
http://bit.ly/13hYcEv
3.9