by Paul Gilster | Jul 12, 2015 | Outer Solar System
A chasm in Charon’s southern hemisphere turns out to be longer and deeper than Earth’s Grand Canyon, says William McKinnon (Washington University, St. Louis), deputy lead scientist with New Horizon’s Geology and Geophysics investigation team.
“This is the first clear evidence of faulting and surface disruption on Charon. New Horizons has transformed our view of this distant moon from a nearly featureless ball of ice to a world displaying all kinds of geologic activity.”
Image: Chasms, craters, and a dark north polar region are revealed in this image of Pluto’s largest moon Charon taken by New Horizons on July 11, 2015. Credit: NASA/JHUAPL/SWRI.
The most prominent crater, near Charon’s south pole, is almost 100 kilometers across, and evidently the result of a geologically recent impact. This NASA news release adds that the darkness of the crater floor may be the result of a different kind of icy material being exposed, less reflective than the ices on the surface. Another possibility: The ice of the crater floor has a larger grain size, reflecting less sunlight. This would be the result of ice melting during the impact event and re-freezing into larger grains.
Image: This annotated version of the Charon imagery includes a diagram showing Charon’s north pole, equator, and central meridian, with the features highlighted. Credit: NASA/JHUAPL/SWRI.
Meanwhile, the dark region near Charon’s north pole bears watching, with more detailed images coming up on the 14th.
by Paul Gilster | Jul 11, 2015 | Outer Solar System |
The side of Pluto that always faces its large moon Charon is the side that New Horizons won’t see when it makes its close flyby on July 14. That makes the image below what principal investigator Alan Stern is calling “the last, best look that anyone will have of Pluto’s far side for decades to come.”
Image: New Horizons’ last look at Pluto’s Charon-facing hemisphere reveals intriguing geologic details that are of keen interest to mission scientists. This image, taken early the morning of July 11, 2015, shows newly-resolved linear features above the equatorial region that intersect, suggestive of polygonal shapes. This image was captured when the spacecraft was 2.5 million miles (4 million kilometers) from Pluto. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute.
Four dark spots seem to be connected to the dark belt in Pluto’s equatorial region, their fairly regular spacing a source of considerable curiosity. The large areas are estimated to be roughly 480 kilometers across, with irregular boundaries between light and dark terrain. Jeff Moore (NASA Ames) gives a glimpse of what’s ahead:
“When we combine images like this of the far side with composition and color data the spacecraft has already acquired but not yet sent to Earth, we expect to be able to read the history of this face of Pluto.”
And of course, as this JHU/APL news release reminds us, we’ll soon be seeing the encounter hemisphere from as close as 12,500 kilometers.
by Paul Gilster | Jul 11, 2015 | Outer Solar System |
Pluto’s surface is beginning to be revealed, with the first signs of geological features, as principal investigator Alan Stern explains:
“Among the structures tentatively identified in this new image are what appear to be polygonal features; a complex band of terrain stretching east-northeast across the planet, approximately 1,000 miles long; and a complex region where bright terrains meet the dark terrains of the whale. After nine and a half years in flight, Pluto is well worth the wait.”
Image: Tantalizing signs of geology on Pluto are revealed in this image from New Horizons taken on July 9, 2015 from 3.3 million miles (5.4 million kilometers) away. At this range, Pluto is beginning to reveal the first signs of discrete geologic features. This image views the side of Pluto that always faces its largest moon, Charon, and includes the so-called “tail” of the dark whale-shaped feature along its equator. (The immense, bright feature shaped like a heart had rotated from view when this image was captured. Among the structures tentatively identified in this new image are what appear to be polygonal features; a complex band of terrain stretching east-northeast across the planet, approximately 1,000 miles long; and a complex region where bright terrains meet the dark terrains of the whale. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute.
The annotated image below includes a reference globe showing Pluto’s orientation, with equator and central meridian in bold.
And the photo below speaks for itself. It’s been nine years. Pluto at last.
Image: Science team members react to the latest New Horizons data from Pluto at the Johns Hopkins University Applied Physics Lab on July 10, 2015. Left to right: Cathy Olkin, Jason Cook, Alan Stern, Will Grundy, Casey Lisse, and Carly Howett. Photo by Michael Soluri.
by Paul Gilster | Jul 10, 2015 | Outer Solar System |
New Horizons makes its closest approach to Pluto, at approximately 12,500 kilometers above the surface, at 0749 EDT (1149 UTC) on Tuesday July 14. Be aware that for much of that day, we’ll be out of communication with the spacecraft while it’s busy gathering data. About 2102 EDT (0102 UTC on the 15th), we should receive a confirmation of a successful flyby — the spacecraft is scheduled to send a preprogrammed signal that it has survived the close approach. Then the data flow begins and will continue for months.
NASA offers the schedule for the flyby here, with information on NASA TV coverage. We should be looking at close-up images of Pluto and hearing early reactions from the science team by mid-afternoon of Wednesday the 15th. And of course it will be possible to follow the mission on Facebook or on Twitter (also #PlutoFlyby). The nail-biting time will be the wait on the 14th for the signal announcing a successful transit of the system. It doesn’t take a large object to silence a spacecraft moving at 14 kilometers per second and we can only hope for the best.
Meanwhile, the imagery keeps improving, with both Pluto and Charon beginning to swim out of the image-processing mist. We’re seeing bright and dark features on Pluto’s surface, while Charon presents a more uniform light gray terrain with a large dark polar region. This NASA news release speculates on the possibility of impact craters on Charon, quoting Jeff Moore (NASA Ames): “If we see impact craters on Charon, it will help us see what’s hidden beneath the surface. Large craters can excavate material from several miles down and reveal the composition of the interior.”
Image: Pluto from the New Horizons’ Long Range Reconnaissance Imager (LORRI), July 8, 2015. Most of the bright features around Pluto’s edge are a result of image processing, but the bright sliver below the dark “whale,” which is also visible in unprocessed images, is real.
The differences between Pluto and Charon are increasingly apparent, with Charon lacking the reddish color of the former, a hue that has reminded some of us of early, blurry photos of Mars. While frozen ices like nitrogen, carbon dioxide and methane have been detected on Pluto, Charon’s surface seems to be mostly frozen water and ammonia compounds. Unlike Pluto, Charon has no atmosphere, and its interior is composed of rock and ice in equal measures, whereas Pluto’s interior is predominantly rock. The lower surface contrast of Charon has been abundantly clear as New Horizons returns images of the two dissimilar worlds.
Image: Image of Charon from the New Horizons’ Long Range Reconnaissance Imager (LORRI), July 8, 2015. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute.
As New Horizons nears its closest approach, the Cassini orbiter will take images of Pluto/Charon from its distant station around Saturn, and beginning July 23, the Spitzer Space Telescope will take seven days of observations at infrared wavelengths. The plan is to study ices on Pluto’s surface. New Horizons will also be backed up by Kepler observations, with the K2 mission focusing on Pluto for a three month period beginning in October.
“K2 observations will expand the time coverage of the speedy New Horizons flyby of Pluto, making observations of the dwarf planet-moon system every 30 minutes,” said Steve Howell, project scientist for Kepler/K2 at NASA’s Ames Research Center in Moffett Field, California. “We are excited to turn the planet-hunting Kepler spacecraft’s attention to this distant solar system object to provide additional scientific insight into this far-off, mysterious world, itself a miniature solar system of five moons in orbit about Pluto.”
Image: New Horizons was about 3.7 million miles (6 million kilometers) from Pluto and Charon when it snapped this portrait late on July 8, 2015. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute.
And we’ve already had one interesting study performed by the SOFIA airborne observatory, an infrared telescope mounted on a 747 aircraft. On June 28, Pluto occulted a distant star, creating a backlighting that could be studied to provide a baseline measurement of Pluto’s atmosphere. All of this, plus the data that the Hubble Space Telescope has gathered about Pluto’s smaller moons, will provide datasets that complement the abundant science return of New Horizons.
Image: This is the same image of Pluto and Charon from July 8, 2015; color information obtained earlier in the mission from the Ralph instrument has been added. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute.
by Paul Gilster | Jul 9, 2015 | Exoplanetary Science |
Not long ago we looked at a new paper from Alan Boss that modeled interactions in young protoplanetary disks (A Disruptive Pathway for Planet Formation). The idea here is that as dust grains and larger objects bump into each other on the way to forming planetesimals, a mechanism must exist to keep them from spiraling into their star. Boss’ models show explosive phases in young stars that lead to gravitational instabilities of the sort needed to scatter these small objects outward and preserve their prospects for forming into planetesimals, and perhaps one day, planets.
Watching infant solar systems form is akin to studying embryology in animal species, a chance to understand the myriad interactions that affect growth and set it in particular directions. Now we have work out of the University of St. Andrews, recently presented at the National Astronomy Meeting in Llandudno, Wales, that announces the discovery of a ring of small rocks circling the star DG Tauri, a 2.5 million year old object some 450 light years from Earth.
Image: An artist’s impression of the belt of ‘pebbles’ in orbit around the star DG Tauri. The inset is a close up view of a section of the belt. Credit: J. Ilee. Adapted from original work by ESO/L. Calçada/M. Kornmesser, ALMA (ESO/NAOJ/NRAO)/L. Calçada (ESO).
The work of Jane Greaves and Anita Richards (University of Manchester) is based on data from the e-MERLIN array of radio telescopes centered in Jodrell Bank (Cheshire) and extending over southern England to form an interferometer, giving it the resolution of a single large telescope. The instrumentation proved up to the considerable challenge, as Greaves relates:
“The extraordinarily fine detail we can see with the e-MERLIN telescopes was the key to this discovery. We could zoom into a region as small as the orbit of Jupiter would be in the Solar System. We found a belt of pebbles strung along a very similar orbit – just where they are needed if a planet is to grow in the next few million years. Although we thought this was how planets must get started, it’s very exciting to actually see the process in action!”
The observations, as this Royal Astronomical Society news release explains, were made at a wavelength of about 4.6 cm. They revealed a signature that requires chunks of rock at least a centimeter in size. This is a useful finding, for as we’ve seen in the work of Alan Boss, we’re in the process of tuning up our computer models of protoplanetary disks and their interactions. Now we can identify, at least in some systems, the location of pebble-like material that will one day accrete into larger objects. A deeper analysis of young disks should emerge from all this.
Image: An e-MERLIN map of the star DG Tauri. The yellow and red areas show what is thought to be a ring of pebble-sized clumps in orbit around the star. Credit: J. Greaves / A. Richards / JCBA.
Studying the results will be, among others, a group called the Planet Earth Building Blocks Legacy e-MERLIN Survey (known by its fitting acronym — PEBBLeS). The team plans to extend studies like this to a number of stars that are in the process of forming their own solar systems. Right now we’re using equipment sensitive to regions as small as Jupiter’s orbit, but the logical goal is to move in five times closer to witness the formation of planets like our own. The researchers believe that upgrades to e-MERLIN and the coming capabilities of the Square Kilometer Array will make such observations possible.
