(being continued from 24/10/14)
Hubble Observes Last Month’s Triple-Moon Conjunction
Yesterday, the Space Telescope Institute released a set of images as well as a movie of Jupiter acquired during a rare triple moon-shadow transit on January 24. During the event, Io, Europa, and Callisto aligned so that the three moons and their shadows appeared to move across the face of Jupiter. The next such triple-event won’t take place until 2025. The Hubble images were even sharp enough to spot some of Io and Callisto’s large scale albedo markings (like the flow field around Io’s Isum Patera or the bright patch in the middle of Callisto’s Asgard impact basin). With a keen eye, you can even spot the small inner moons, Amalthea and Thebe, and their shadows as two pairs of faint dark spots passing between Io and Callisto against the bright equatorial zone.
The difference in the crispness of the moons’ shadows results from their different distances from Jupiter. Io is much closer to Jupiter than Callisto, so when it easily eclipses the Sun when it passes in front of it in Jupiter’s sky. Callisto is farther away, so it appears to be closer in size to the Sun so there is a more narrow zone where it completely eclipses it (the umbra) and a wider zone where only a partial eclipse occurs (the penumbra), similar to solar eclipses on the Earth.
Opposition for Jupiter is today, and now that the moon is moving further away from Jupiter in the night sky, this is a great time to observe it and its Galilean satellites. Great ground-based images are showing up, including these sets taken by Anthony Wesley and Christopher Go.
Link: Hubble Captures Rare Triple-Moon Conjunction [hubblesite.org]
Link: ALPO-Jupiter Images from February 5 [alpo-j.asahikawa-med.ac.jp]
Io Volcano Observer Proposal
The deadline for NASA’s Discovery proposals was this week. 28 proposals were submitted with targets ranging from Phobos and Deimos, to Venus, to asteroids like metallic 16 Psyche, and even Enceladus. Of course, the one that Ionians will be pulling for is the Io Volcano Observer (IVO), proposed by a team led by the University of Arizona’s Alfred McEwen and managed by John Hopkins’ Applied Physics Lab, which is making its second go around after also being submitted for the 2010 Discovery Announcement of Opportunity (AO). The Martian lander, InSight, was ultimately chosen after that AO over a great set of proposed missions, which included a boat that would’ve sailed around Titan’s great Kraken Mare.
IVO, if selected this time around, would launch in late May 2021 with an arrival at Jupiter in February 2026 after a 510 km altitude flyby of Io. IVO would remain in an elliptical, inclined orbit around Jupiter, flying by Io eight more times during the nominal mission between August 2026 and late December 2027. An extended mission with nearly year-long orbits is possible, providing high-resolution, imaging coverage of Io’s leading hemisphere in daylight as well as collaboration with the JUICE spacecraft. Unlike the 2010 proposal, this year’s would make use of advanced, roll-out solar panels to power the probe and its five instruments, instead of the Advanced Sterling Radioisotope Generators that are unavailable to proposal teams this time around. These instruments include: two cameras, one narrow-angle and the other wide-angle (NAC and WAC); a Thermal Mapper (TMAP); Dual Fluxgate Magnetometers (DMAG); and a suite of particle instruments (PEPI), which includes an ion and neutral mass spectrometer (INMS) and a Plasma Ion Analyzer (PIA). There is also the potential for an add-on, student collaboration instrument, a wide-angle, near-infrared camera named HOTMAP. While the WAC, PEPI, and HOTMAP will be bolted to the spacecraft, the NAC and TMAP will be on a ± 90° pivot, allowing for off-nadir pointing of those instruments without turning the entire spacecraft.
The mission’s main goals include mapping Io’s active volcanism on a more global scale than Galileo and Voyager were able to obtain, measuring Io’s induced magnetic field at different points in its orbit around Jupiter to provide a better estimate for the thickness, distribution, and melt percentage of its magma ocean, mapping Io’s topography including its numerous mountains, and measuring the composition of the volcanic gases that are released from Io’s interior. During two of its flybys (I0 and I2), IVO will acquire gravity science using 2-Way Doppler tracking, which combined with the gravity data acquired during a few of Galileo’s encounters with Io, will constrain our knowledge of mantle rigidity. The mission will also act as a technology demonstration for Deep Space Optical Communications, which could substantial increase the data return of future missions.
On each orbit, IVO will spend a week acquiring images of Io, allowing it to map Io so changes at its many volcanoes can be observed and to monitor hot spots and auroral emissions during four different eclipses. IVO would also use this time to help look for Europa’s elusive plumes in support of Europa Clipper, which should arrive at Jupiter shortly after IVO. During the 24 hours around closest approach, while IVO approaches and departs from Io over its polar regions, IVO will acquire several NAC mosaics of Io along with TMAP images to map heat flow and monitor volcanism. The NAC will also be used to acquire movies of active plumes like Pele and Marduk. Finally, right at closest approach, the spacecraft will acquire WAC, NAC, TMAP, and maybe HOTMAP imaging swaths along with INMS mass spectra and DMAG/PIA measurements as IVO sweeps north across Io. At least 20 Gb of data (100x the Io data returned by Galileo) would be acquired during each encounter and will be played back during the apojove part of each orbit (distant monitoring observations will also be acquired to help watch for new major eruptions).
More information about this exciting mission can be found in an abstract submitted to next month’s Lunar and Planetary Sciences Conference. A fact sheet with even more details about Io Volcano Observer is also available. NASA expects to select three (or so) finalists for Phase A studies in September with a final selection from those sometime next year.
Link: The Io Volcano Observer (IVO) for Discovery 2015 [www.hou.usra.edu]
Link: Io Volcano Observer Public Fact Sheet [pirlwww.lpl.arizona.edu]
Posted by Jason Perry
(TO BE CONTINUED)
SOURCE http://www.gishbartimes.org/ /