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Space News Update — September 27, 2016 —
Contents
In the News
Story 1:
NASA’s Hubble Spots Possible Water Plumes Erupting on Jupiter's Moon Europa
Story 2:
NASA’s Asteroid-Bound Spacecraft Aces Instrument Check
Story 3:
Pluto’s ‘Heart’ Sheds Light on a Possible Buried Ocean
Departments
The Night Sky
ISS Sighting Opportunities
NASA-TV Highlights
Space Calendar
Food for Thought
Space Image of the Week
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1. NASA’s Hubble Spots Possible Water Plumes Erupting on Jupiter's Moon Europa
This composite image shows suspected plumes of water vapor erupting at the 7 o’clock position off the limb of Jupiter’s
moon Europa. The plumes, photographed by NASA’s Hubble’s Space Telescope Imaging Spectrograph, were seen in
silhouette as the moon passed in front of Jupiter. Hubble’s ultraviolet sensitivity allowed for the features -- rising over 100
miles (160 kilometers) above Europa’s icy surface -- to be discerned. The water is believed to come from a subsurface
ocean on Europa. The Hubble data were taken on January 26, 2014. The image of Europa, superimposed on the Hubble
data, is assembled from data from the Galileo and Voyager missions. Credits: NASA/ESA/W. Sparks (STScI)/USGS
Astrogeology Science Center
Astronomers using NASA's Hubble Space Telescope have imaged what may be water vapor plumes erupting
off the surface of Jupiter's moon Europa. This finding bolsters other Hubble observations suggesting the icy
moon erupts with high altitude water vapor plumes.
The observation increases the possibility that missions to Europa may be able to sample Europa’s ocean
without having to drill through miles of ice.
“Europa’s ocean is considered to be one of the most promising places that could potentially harbor life in the
solar system,” said Geoff Yoder, acting associate administrator for NASA’s Science Mission Directorate in
Washington. “These plumes, if they do indeed exist, may provide another way to sample Europa’s subsurface.”
The plumes are estimated to rise about 125 miles (200 kilometers) before, presumably, raining material back
down onto Europa's surface. Europa has a huge global ocean containing twice as much water as Earth’s
oceans, but it is protected by a layer of extremely cold and hard ice of unknown thickness. The plumes provide
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a tantalizing opportunity to gather samples originating from under the surface without having to land or drill
through the ice.
The team, led by William Sparks of the Space Telescope Science Institute (STScI) in Baltimore observed these
finger-like projections while viewing Europa's limb as the moon passed in front of Jupiter.
The original goal of the team's observing proposal was to determine whether Europa has a thin, extended
atmosphere, or exosphere. Using the same observing method that detects atmospheres around planets
orbiting other stars, the team realized if there was water vapor venting from Europa’s surface, this observation
would be an excellent way to see it.
"The atmosphere of an extrasolar planet blocks some of the starlight that is behind it," Sparks explained. "If
there is a thin atmosphere around Europa, it has the potential to block some of the light of Jupiter, and we
could see it as a silhouette. And so we were looking for absorption features around the limb of Europa as it
transited the smooth face of Jupiter."
In 10 separate occurrences spanning 15 months, the team observed Europa passing in front of Jupiter. They
saw what could be plumes erupting on three of these occasions.
NASA's Hubble Space Telescope took direct ultraviolet images of the icy moon Europa transiting across the
disk of Jupiter. Out of 10 observations, Hubble saw what may be water vapor plumes on three of the images.
This adds another piece of supporting evidence to the existence of water vapor plumes on
This work provides supporting evidence for water plumes on Europa. In 2012, a team led by Lorenz Roth of
the Southwest Research Institute in San Antonio, detected evidence of water vapor erupting from the frigid
south polar region of Europa and reaching more than 100 miles (160 kilometers) into space. Although both
teams used Hubble's Space Telescope Imaging Spectrograph instrument, each used a totally independent
method to arrive at the same conclusion.
"When we calculate in a completely different way the amount of material that would be needed to create
these absorption features, it's pretty similar to what Roth and his team found," Sparks said. "The estimates for
the mass are similar, the estimates for the height of the plumes are similar. The latitude of two of the plume
candidates we see corresponds to their earlier work."
But as of yet, the two teams have not simultaneously detected the plumes using their independent techniques.
Observations thus far have suggested the plumes could be highly variable, meaning that they may sporadically
erupt for some time and then die down. For example, observations by Roth’s team within a week of one of the
detections by Sparks’ team failed to detect any plumes.
If confirmed, Europa would be the second moon in the solar system known to have water vapor plumes. In
2005, NASA's Cassini orbiter detected jets of water vapor and dust spewing off the surface of Saturn's moon
Enceladus.
Scientists may use the infrared vision of NASA’s James Webb Space Telescope, which is scheduled to launch in
2018, to confirm venting or plume activity on Europa. NASA also is formulating a mission to Europa with a
payload that could confirm the presence of plumes and study them from close range during multiple flybys.
“Hubble’s unique capabilities enabled it to capture these plumes, once again demonstrating Hubble’s ability to
make observations it was never designed to make,” said Paul Hertz, director of the Astrophysics Division at
NASA Headquarters in Washington. “This observation opens up a world of possibilities, and we look forward to
future missions -- such as the James Webb Space Telescope -- to follow up on this exciting discovery.”
The work by Sparks and his colleagues will be published in the Sept. 29 issue of the Astrophysical Journal.
Source: NASA Return to Contents
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2. NASA’s Asteroid-Bound Spacecraft Aces Instrument Check
Its science instruments have been powered on, and NASA’s OSIRIS-REx spacecraft continues on its journey to an
asteroid. The spacecraft has passed its initial instrument check with flying colors as it speeds toward a 2018
rendezvous with the asteroid Bennu.
Last week NASA’s spacecraft designed to collect a sample of an asteroid ran the first check of its onboard
instruments. Starting on Sept. 19, engineers controlling the Origins, Spectral Interpretation, Resource Identification,
Security-Regolith Explorer (OSIRIS-REx) spacecraft powered on and operated the mission’s five science instruments
and one of its navigational instruments. The data received from the checkout indicate that the spacecraft and its
instruments are all healthy.
Instrument testing commenced with the OSIRIS-REx Camera Suite (OCAMS), provided by the University of Arizona.
On Monday, OCAMS executed its power-on and test sequence with no issues. The cameras recorded a star field in
Taurus north of the constellation Orion along with Orion’s bright red star Betelgeuse. The three OCAMS cameras
performed flawlessly during the test.
On Monday and Wednesday, the OSIRIS-REx Laser Altimeter (OLA), contributed by the Canadian Space Agency,
conducted its test sequences, which included a firing of its laser. All telemetry received from the OLA instrument
was as expected.
On Tuesday, both the OSIRIS-REx Visible and Infrared Spectrometer (OVIRS), provided by NASA’s Goddard Space
Flight Center, and the OSIRIS-REx Thermal Emissions Spectrometer (OTES), provided by Arizona State University,
were separately powered on for tests. Data from both during the checkout showed that the instruments were
healthy. The science measurements acquired from OTES exceeded the instrument’s performance requirements.
On Wednesday, the student experiment from MIT, the Regolith X-ray Imaging Spectrometer (REXIS), executed its
functional test with no problems. And on Thursday, the Touch and Go Camera System (TAGCAMS) navigational
camera was powered on and tested, and it operated as expected. As part of its checkout, TAGCAMS took an image
of the spacecraft’s Sample Return Capsule.
The downlink of the test data continued through Sunday via the spacecraft’s low gain antenna (LGA), which
transmitted at 40 kbps to NASA’s Deep Space Network.
Source: NASA Return to Contents
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3. Pluto’s ‘Heart’ Sheds Light on a Possible Buried Ocean
Credits: NASA/APL/SwRI
Ever since NASA’s New Horizons spacecraft flew by Pluto last year, evidence has been mounting that the dwarf
planet may have a liquid ocean beneath its icy shell. Now, by modeling the impact dynamics that created a
massive crater on Pluto’s surface, a team of researchers has made a new estimate of how thick that liquid
layer might be.
The study, led by Brown University geologist Brandon Johnson and published in Geophysical Research Letters,
finds a high likelihood that there’s more than 100 kilometers of liquid water beneath Pluto’s surface. The
research also offers a clue about the composition of that ocean, suggesting that it likely has a salt content
similar to that of the Dead Sea.
“Thermal models of Pluto’s interior and tectonic evidence found on the surface suggest that an ocean may
exist, but it’s not easy to infer its size or anything else about it,” said Johnson, who is an assistant professor in
Brown’s Department of Earth, Environmental and Planetary Sciences. “We’ve been able to put some
constraints on its thickness and get some clues about composition.”
The research focused on Sputnik Planum, a basin 900 kilometers across that makes up the western lobe the
famous heart-shaped feature revealed during the New Horizons flyby. The basin appears to have been created
by an impact, likely by an object 200 kilometers across or larger.
The story of how the basin relates to Pluto’s putative ocean starts with its position on the planet relative to
Pluto’s largest moon, Charon. Pluto and Charon are tidally locked with each other, meaning they always show
each other the same face as they rotate. Sputnik Planum sits directly on the tidal axis linking the two worlds.
That position suggests that the basin has what’s called a positive mass anomaly — it has more mass than
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average for Pluto’s icy crust. As Charon’s gravity pulls on Pluto, it would pull proportionally more on areas of
higher mass, which would tilt the planet until Sputnik Planum became aligned with the tidal axis.
But a positive mass anomaly would make Sputnik Planum a bit of an odd duck as craters go.
“An impact crater is basically a hole in the ground,” Johnson said. “You’re taking a bunch of material and
blasting it out, so you expect it to have negative mass anomaly, but that’s not what we see with Sputnik
Planum. That got people thinking about how you could get this positive mass anomaly.”
Part of the answer is that, after it formed, the basin has been partially filled in by nitrogen ice. That ice layer
adds some mass to the basin, but it isn’t thick enough on its own to make Sputnik Planum have positive mass,
Johnson says.
The rest of that mass may be generated by a liquid lurking beneath the surface.
Like a bowling ball dropped on a trampoline, a large impact creates a dent on a planet’s surface, followed by a
rebound. That rebound pulls material upward from deep in the planet’s interior. If that upwelled material is
denser than what was blasted away by the impact, the crater ends up with the same mass as it had before the
impact happened. This is a phenomenon geologists refer to as isostatic compensation.
Water is denser than ice. So if there were a layer of liquid water beneath Pluto’s ice shell, it may have welled
up following the Sputnik Planum impact, evening out the crater’s mass. If the basin started out with neutral
mass, then the nitrogen layer deposited later would be enough to create a positive mass anomaly.
“This scenario requires a liquid ocean,” Johnson said. “We wanted to run computer models of the impact to
see if this is something that would actually happen. What we found is that the production of a positive mass
anomaly is actually quite sensitive to how thick the ocean layer is. It’s also sensitive to how salty the ocean is,
because the salt content affects the density of the water.”
The models simulated the impact of an object large enough to create a basin of Sputnik Planum’s size hitting
Pluto at a speed expected for that part in the solar system. The simulation assumed various thicknesses of the
water layer beneath the crust, from no water at all to a layer 200 kilometers thick.
The scenario that best reconstructed Sputnik Planum’s observed size depth, while also producing a crater with
compensated mass, was one in which Pluto has an ocean layer more than 100 kilometers thick, with a salinity
of around 30 percent.
“What this tells us is that if Sputnik Planum is indeed a positive mass anomaly —and it appears as though it is
— this ocean layer of at least 100 kilometers has to be there,” Johnson said. “It’s pretty amazing to me that
you have this body so far out in the solar system that still may have liquid water.”
As researchers continue to look at the data sent by New Horizons, Johnson is hopeful that a clearer picture of
Pluto’s possible ocean will emerge.
Johnson’s co-authors on the paper were Timothy Bowling of the University of Chicago and Alexander
Trowbridge and Andrew Freed from Purdue University.
Source: Brown University Return to Contents
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The Night Sky
Source: Sky and Telescope Return to Contents
Friday, September 30
This is the time of year when the Little Dipper extends left from Polaris after dark. The Little Dipper's only
two bright stars are Polaris, the end of the Dipper's handle, and Kochab, the lip of its bowl. Both are 2nd
magnitude. They're exactly level with each other about a half hour after dark now, depending on your
latitude.
New Moon (exact at 8:11 p.m. Eastern Daylight Time).
Saturday, October 1
• As Deneb takes over from Vega as the star at the zenith after dark (for mid-northern latitudes), dim
Capricornus takes over from Sagittarius as the zodiacal constellation standing due south. It is ever thus.
As dawn brightens in the east, the crescent Moon wanes and steps lower past Regulus and Mercury
on successive mornings.
Tuesday, September 27
This is the time of year when, during the evening,
the dim Little Dipper "dumps water" into the bowl
of the Big Dipper way down below. The Big Dipper
will dump it back in the evenings of spring.
As dawn brightens Wednesday morning the 28th,
spot the thin crescent Moon between Regulus
above it and Mercury below it, as shown at right.
Wednesday, September 28
As dawn brightens Thursday morning the 29th,
look for a super-thin crescent Moon near Mercury
very low in the east. Start looking about 45
minutes before your local sunrise time. Binoculars
will help as dawn grows bright.
Thursday, September 29
The Two Top Miras. Chi Cygni now overhead in
the evening, and Mira (Omicron Ceti) visible late
at night, are the two brightest Mira-type stars in
the sky: long-period red variables. Chi Cyg should
be at or just past its maximum brightness, 5th
magnitude or so. Mira should be nearly at its
minimum, 8th or 9th mag. Follow them through
the coming months with the article and finder
charts in the October Sky & Telescope, page 49.
As one brightens and the other dims, when will
they pass each other in brightness?
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ISS Sighting Opportunities (from Denver)
Date Visible Max Height Appears Disappears
Tue Sep 27, 7:31 PM 2 min 13° 10° above SSE 12° above ESE
Tue Sep 27, 9:05 PM < 1 min 12° 10° above WSW 12° above WSW
Wed Sep 28, 8:13 PM 3 min 66° 10° above SW 66° above SSE
Thu Sep 29, 7:21 PM 6 min 31° 10° above SSW 11° above ENE
Thu Sep 29, 8:59 PM < 1 min 21° 18° above WNW 21° above WNW
Fri Sep 30, 8:07 PM 3 min 48° 26° above W 25° above NNE
Sighting information for other cities can be found at NASA’s Satellite Sighting Information
NASA-TV Highlights (all times Eastern Time Zone)
Wednesday, September 28
12 p.m. - ISS Expedition 49 In-Flight Interview with the NBC “Meet the Press” Podcast with Chuck Todd and NASA Flight Engineer Kate Rubins (all channels)
Thursday, September 29
11:30 a.m., - ISS Expedition 49 In-Flight Interview with Cosmopolitan.com and NASA Flight Engineer Kate Rubins (starts at 11:45 a.m.) (all channels)
Friday, September 30
6 a.m. - NASA Joins Rosetta End of Mission coverage from European Space Operations Centre (ESOC), Darmstadt, Germany (Starts at 6:15 a.m.) (all channels)
Watch NASA TV online by going to the NASA website. Return to Contents
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Space Calendar
Sep 27 - Cassini, Titan Flyby
Sep 27 - Comet 73P-BH/Schwassmann-Wachmann Perihelion (1.005 AU)
Sep 27 - Comet 73P-BI/Schwassmann-Wachmann Perihelion (1.005 AU)
Sep 27 - Comet 73P-BM/Schwassmann-Wachmann Perihelion (1.005 AU)
Sep 27 - Comet 73P-BP/Schwassmann-Wachmann Perihelion (1.005 AU)
Sep 27 - Comet 175P/Hergenrother At Opposition (3.906 AU)
Sep 27 - Comet C/2015 V3 (PANSTARRS) At Opposition (4.281 AU)
Sep 27 - Apollo Asteroid 2016 SG Near-Earth Flyby (0.060 AU)
Sep 27 - Amor Asteroid 2016 QB2 Near-Earth Flyby (0.081 AU)
Sep 27 - Asteroid 10168 Stony Ridge Closest Approach To Earth (1.583 AU)
Sep 27 - Asteroid 243097 Batavia Closest Approach To Earth (1.641 AU)
Sep 27 - Asteroid 2791 Paradise Closest Approach To Earth (1.701 AU)
Sep 27 - Asteroid 54522 Menaechmus Closest Approach To Earth (1.945 AU)
Sep 27 - Plutino 469372 (2001 QF298) At Opposition (42.405 AU)
Sep 28 - Mercury At Its Greatest Western Elongation (18 Degrees)
Sep 28 - Comet 73P-BA/Schwassmann-Wachmann Perihelion (1.005 AU)
Sep 28 - Comet P/2008 SH164 (LINEAR) At Opposition (2.174 AU)
Sep 28 - Comet 250P/Larson At Opposition (2.778 AU)
Sep 28 - Apollo Asteroid 6239 Minos Closest Approach To Earth (0.945 AU)
Sep 28 - Asteroid 2041 Lancelot Closest Approach To Earth (1.662 AU)
Sep 28 - Asteroid 4149 Harrison Closest Approach To Earth (1.904 AU)
Sep 28 - Asteroid 904 Rockefellia Closest Approach To Earth (1.958 AU)
Sep 29 - Moon Occults Mercury
Sep 29 - Comet 263P/Gibbs At Opposition (2.413 AU)
Sep 29 - Asteroid 11 Parthenope At Opposition (8.9 Magnitude)
Sep 29 - Asteroid 705 Erminia Occults HIP 44331 (6.5 Magnitude Star)
Sep 29 - Apollo Asteroid 3200 Phaethon Closest Approach To Earth (0.402 AU)
Sep 29 - Asteroid 8553 Bradsmith Closest Approach To Earth (1.180 AU)
Sep 29 - Asteroid 1855 Korolev Closest Approach To Earth (1.434 AU)
Sep 30 - Rosetta, Crash Landing on Comet 67P/Churyumov-Gerasimenko
Sep 30 - Kepler, End of Extended Mission
Sep 30 - Swift, End of Extended Mission
Source: JPL Space Calendar Return to Contents
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Food for Thought
Incoming! New Warning System Tracks Potentially Dangerous Asteroids
On Feb. 15, 2013, a meteor exploded over the city of Chelyabinsk, Russia. Scientists created reconstructions of the meteor
explosion to help refine models on the frequency of such asteroid impacts. Photo by Olga Krugolva/CC BY-NC-ND 2.0
A new early warning system may help speed up calculations of when and where incoming asteroids could strike
Earth.
By monitoring observations of newly reported space objects, a computer program called Scout can quickly identify
potentially dangerous asteroids, then automatically call for follow-ups to calculate a more precise path for these
bodies, researchers said.
"These are objects that observers have reported, and they suspect them to be asteroids," Paul Chodas, manager of
NASA's Center for Near-Earth Object (NEO) Studies at the Jet Propulsion Laboratory (JPL) in California, told
Space.com. "They are most likely asteroids, but they need to be confirmed by other observers."
While midsize asteroids are frequently identified well before they hit Earth, smaller objects can be more difficult to
spot and classify ahead of time. Correctly classifying these objects and determining their orbits takes multiple
observations, researchers have said. And, especially for potentially hazardous impactors, the sooner the better, the
researchers said.
On Oct. 7, 2008, an 80-ton rock plowed through Earth's atmosphere and exploded above a remote area in Sudan.
The asteroid, known as 2008 TC3, was spotted just 19 hours before it reached the African desert, making this the
first incoming object tracked before crashing into Earth.
But the short notice provided little time for astronomers to follow up. With this in mind, NEO researcher Davide
Farnocchia, also at JPL, worked to create a program to automatically monitor new observations and alert fellow
astronomers.
"If Scout had been in observation eight years ago, it would have given early warning to observers that the asteroid
— eventually named 2008 TC3 — should be followed up immediately because it had the possibility of hitting Earth,"
Chodas said.
Another object, which crashed into Earth's atmosphere around New Year's Day in 2014, wasn't identified until after
it had already collided, burning up in the air over West Africa.
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"Those two events made it clear what was needed and how necessary it was to automate [the process]," Chodas
said.
When astronomers spotted a 10- to 30-foot (3 to 9 meters) space rock in November 2015, Scout took only 45
minutes to determine that the object would brush past Earth without colliding, Farnocchia said at a conference
earlier this year. The asteroid buzzed past Earth a day after being discovered. In contrast, 2008 TC3 wasn't
confirmed as an impactor until 12 hours before it hit Sudan.
Thanks to Scout, when astronomers spot a new object, "we will know sooner that it's a hazardous object," Chodas
said.
When an astronomer identifies an interesting object, he or she posts observations on a website hosted by the Minor
Planet Center (MPC) in Cambridge, Massachusetts. Other astronomers can use that information to study the object,
learning more about it and its orbit. But all of that takes time; astronomers need to check the DPS website
regularly, and if the observations were posted from different time zones, researchers might not see new ones for
several hours. For objects about to collide with Earth, those hours can be critical.
Scout automatically reviews the MPC's website. When a new object is posted, it takes Scout about 10 minutes to
calculate the object's potential paths. If the newfound rock has the potential to threaten the planet, Scout alerts
participating astronomers by email and text of the need for follow-up observations.
Observers around the globe can then head to their telescopes, track the object and post their own updated
observations on the MPC's page. Scout continues to review the page, refining its calculations of the object's orbit
and continuing to send messages as long as the rock remains potentially harmful.
"In many cases, after a few more observations, we realize it's not high priority, because it's not going to come as
close as suspected," Chodas said. "That happens quite often."
The warning time for an impactor varies based on how large it is and how early it is observed, Chodas. Larger
objects are brighter and more likely to be picked up earlier by asteroid-search programs, he said.
At 13 feet (4.1 m) wide, 2008 TC3 was small enough to escape notice until just before it exploded over Sudan.
Some larger objects can escape notice if they follow certain paths through space. Scientists think the asteroid that
exploded without warning over the Russian city of Chelyabinsk in February 2013, wounding more than 1,200
people, was about 65 feet (20 m) wide. The asteroid managed to avoid detection because it approached Earth from
the sunward side and was therefore hidden by the sun's glare.
Had the Chelyabinsk object been a bit larger, Chodas said, it could have potentially been detected months earlier,
when it could have been seen on the nightside of Earth.
Chelyabinsk-size impactors are rare, hitting Earth about once every 80 years or so, Chodas said. In contrast,
smaller, 3-foot (1 m) objects come by fairly frequently, sometimes turning into bright fireballs as they burn up in
Earth's atmosphere. Initial estimates of 2008 TC3 suggested that it had burned up completely, though these
estimates were proven wrong as the asteroid rained down more than 600 chunks of rock into the desert.
Scout tracks only objects whose status as asteroids has not yet been confirmed. Once the Minor Planet Center
classifies a body as an asteroid, the object is moved to another page where it is monitored instead by a program
called Sentry.
Sentry is a long-term impact-monitoring system that continues to track space objects. While Scout looks only about
a month in the future, Sentry peers about a decade ahead. The newfound object should be confirmed and passed
from Scout to Sentry fairly quickly, and the long-range program will then alert astronomers about future impacts,
Chodas said.
Source: Space.com Return to Contents
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Space Image of the Week
Explanation: What makes this cosmic eye look so red? Dust. The featured image from the robotic Spitzer Space Telescope shows infrared light from the well-studied Helix Nebula (NGC 7293) a mere 700 light-years away in the constellation of the Water Carrier Aquarius. The two light-year diameter shroud of dust and gas around a central white dwarf has long been considered an excellent example of a planetary nebula, representing the final stages in the evolution of a Sun-like star. But the Spitzer data show the nebula's central star itself is immersed in a surprisingly bright infrared glow. Models suggest the glow is produced by a dust debris disk. Even though the nebular material was ejected from the star many thousands of years ago, the close-in dust could have been generated by collisions in a reservoir of objects analogous to our own solar system's Kuiper Belt or cometary Oort cloud. Had the comet-like bodies formed in the distant planetary system, they would have survived even the dramatic late stages of the star's evolution.
Source: NASA APOD Return to Contents
The Helix Nebula in Infrared Image Credit: NASA, JPL-Caltech, Spitzer Space Telescope; Processing: Judy Schmidt
