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Deep Space Digest – July 18

Venus Express survives the atmosphere, Curiosity examines a meteorite, Rosetta finds an odd comet, Cassini looks at rings, and New Horizons draws within a year of Pluto.

In the News:

Venus Express

Venus Express survived its aerobraking campaign, and has begun the process of reboosting its pericenter from 129.1km to a target of 460km. As of July 18, pericenter was at an altitude of 300km. One fear was that the Venus Express would not have the propellant needed to survive the campaign. Indeed, the ESA’s current dead reckoning suggests that the spacecraft has only 8.65kg of propellant left, less than 2% of the 570kg of propellant it was launched with. However, it appears that the probe will have enough to complete the reboost, which delays the end of Venus Express’s mission until late this year or early next year.

Some preliminary results from the aerobraking campaign have been released, which are detailed in this ESA blog post. One of the most important findings is that Venus’s atmospheric density is incredibly variable. In some passes, atmospheric drag slowed the spacecraft up to 1m/s more than otherwise identical passes. ESA researchers are confident that these differences are the result of weather – the question is which kind. Since Venus lacks a magnetic field, it is possible that changes in the solar wind could be compressing the atmosphere. Alternatively, it could be atmospheric waves created by weather systems deeper in the cloud decks. Even in its final months, Venus Express is still providing valuable information from the planet.

Also, be sure to check out this Google Hangout with some of the scientists and engineers behind Venus Express.

Time since launch: 3174 days
Time elapsed time in Venus orbit: 2921 days
Light travel time to Earth: 12 minutes, 22 seconds


Curiosity continues trundling its way towards Mt. Sharp. Since a check-up on the rovers wheels turned up significant wear and tear earlier this year, its operators have tried to keep the rover on routes with softer sand. This week it became clear that Curiosity was going to have to make a traverse over 200m of caprock terrain, which is an area of exposed bedrock with sharp erosional features. It was caprock terrain that damaged Curiosity’s wheels in the first place, although the rover’s operators have a better handle on how to minimize the damage. Still, it will be slow going for the rover until it makes it through to the other side of the caprock terrain and reaches another stretch of sand that the Curiosity team has dubbed “Hidden Valley”.

It hasn’t been all bad news for the rover during the last couple of weeks, though. Analysis of Curiosity’s meteorite find on May 25 suggests that it is one of the largest ever found on Mars. Named “Lebanon” by the Curiosity science team, the nickel-iron meteorite measures nearly 2 meters across. Unusual cavities were found inside the meteorite, leading some scientists to suggest that the meteorite is of a type called a Pallasite. The cavities may be the result of wind weathering out the softer olivine crystals inside the meteorite.

NASA also released a video produced by Curiosity as it zapped a rock target named “Nova” with its ChemCam laser. Small sparks can be seen on the rock as the high-powered laser heats part of the rock to temperatures comparable to those found in lightning bolts. The heat vaporizes the rock, producing a cloud of plasma that is analyzed by a spectrographic camera onboard Curiosity.

Time since launch: 980 days
Total elapsed time on Mars: 690 sols (711 Earth days)
Light travel time to Earth: 9 minutes, 12 seconds



Rosetta is now on 67P/Churyumov-Gerasimenko’s doorstep. The spacecraft is less than 10,000km from the comet, and only two weeks remain before it performs its orbital insertion burn. Rosetta has peformed two burns during the update period, the first of which came on July 9. That burn took about 46 minutes and slowed Rosetta’s approach to the comet by 25m/s. The second burn occurred on July 16, which slowed Rosetta by another 11m/s over the course of a 26 minutes. Only three burns remain before orbital insertion, the next of which will occur on July 23.

As Rosetta approached the comet, its imaging resolution has increased to the point that we’ve begun to see details of its surface. The most shocking find so far is that 67P appears to be a contact binary – that is, two separate bodies that collided at low speed and “stuck” together. The public release of these images kicked off a small kerfluffle, since they were leaked a day early by the BBC. The leak spurred a response detailing and explaining the ESA’s science data policy. The problem is a delicate balance of making the data public – Rosetta was paid for with public funds – and making sure the scientists who have dedicated a decade of their careers working on Rosetta get due scientific priority for discoveries.

Time since launch: 3791 days
Current distance from 67P/Churyumov-Gerasimenko: less than 10,000km (~6,200 miles)
Current distance from Earth: 405 million km (251 million miles); light travel time: 22 minutes 30 seconds



On July 2, Cassini scientists released the most detailed model for Titan’s interior yet, based on over 100 flybys of the moon which measured its physical properties. One of the most interesting findings is that Titan’s interior ocean is freezing solid, and that a high density for the liquid is needed to explain some of Cassini’s observations. This implies a very salty ocean, perhaps as salty as the Dead Sea. The freezing ocean also explains the apparent lack of cryovolcanism on Titan, as eruptions of water and gas from the interior are likely to be widely scattered and intermittent.

For the last couple of weeks, Cassini has been hanging out high over Saturn’s northern hemisphere. On July 3-5, Cassini used its Cosmic Dust Analyzer instrument to look for dust that was orbiting Saturn in a retrograde direction, or in a direction opposite to the planet’s rotation. On July 6, it turned towards Saturn’s rings, looking at a known ring arc that was backlit by the Sun. This viewing angle increases the brightness of the ring dramatically, making it easier to study. The next day, Cassini turned its eyes towards the irregular moon Kiviuq, which occupies a highly inclined orbit 11 million miles from Saturn.

After orbital tracking on July 8, Cassini performed a couple of instrument calibrations; a magnetometer calibration was performed on the 9th, and a special calibration for the Composite Infrared Spectrometer (CIRS) on the 10th. The CIRS calibration was performed to help with the analysis of Titan observations made by the Herschel Space Observatory before it was shut down. Cassini spent much of the 13th tracking some of Saturn’s moons to help refine their orbits, then turned its Ultraviolet Imaging Spectrograph (UVIS) towards Dione and Enceladus to measure the amount of UV light reflected on their leading hemispheres. On the 14th, the main goal of observations was to make a movie of Saturn’s D-ring, the innermost ring. Then, on the 15th, Cassini again turned towards Saturn’s north pole to watch for auroras, this time in an observation campaign coordinated with the Hubble Space Telescope and the Keck Observatory in Hawaii.

On July 20, Cassini will perform a flyby of Titan. This flyby will mostly focus on UV observations of Titan’s atmosphere.

Time since launch: 6114 days
Total time at Saturn: 3670 days
Light travel time: 1 hour, 19 minutes


New Horizons

On July 14, only a year separated New Horizons from its flyby of Pluto. That same day, the probe performed a short burn designed to keep it on the correct course for the flyby. For the next five weeks, the probe will be performing its yearly instrument checkouts and calibrations before being placed back into hibernation until early next year.

Time since launch: 3103 days
Current distance from Pluto: 429 million kilometers (266 million miles)
Current distance from Earth: 4.32 billion kilometers (2.69 billion miles); light travel time: 4 hours, 0 minutes


Other missions:


MESSENGER is continuing its low-altitude imaging campaign, the final phase of its mission. During this phase it will make passes within 25 miles of Mercury’s north pole, producing images with resolution greater than 10m/pixel. Fuel to maintain the spacecraft’s orbit will run out late this year, and MESSENGER will crash into Mercury sometime during March 2015. Mission operators released a short press release about new insights into high-energy processes on the Sun using MESSENGER and STEREO data.

Time since launch: 3636 days
Total elapsed time in Mercury orbit: 1218 days
Light travel time to Earth: 8 minutes, 19 seconds


Chang’e 3/Yutu

The Sun has just set on Chang’e 3 and Yutu’s landing site in Mare Imbrium, but no updates on the mission’s status have been released by the Chinese space agency.

Time since launch: 230 days
Time since landing: 217 days



Opportunity is working along the west rim of Endeavor Crater on Mars. No news was released by the rover team during this update period.

Time since launch: 4030 days
Total elapsed time on Mars: 3727 sols (3827 Earth days)
Total roving distance: 39.59km (24.60 miles)
Light travel time to Earth: 9 minutes, 12 seconds



MAVEN finished its cruise-phase instrument checkouts on July 17. The probe was placed into hibernation in preparation for orbital insertion on September 22, 2014.

Time since launch: 242 days
Current distance from Mars: 16.9 million kilometers (10.5 million miles)
Current distance from Earth: 148.9 million kilometers (92.5 million miles); light travel time: 8 minutes, 16 seconds


Mars Orbiter Mission

ISRO celebrated the fact that their Mars Orbiter Mission had made it 75% of the way to Mars on July 4. So far, the success of the mission has led the Indian space agency to consider a follow-up mission to Mars between 2017 and 2020. India’s first Mars mission is currently en route to the Red Planet, where it will arrive on September 24, 2014.

Time since launch: 255 days
Current distance from Mars: 17.4 million kilometers (10.8 million miles)
Current distance from Earth: 148.4 million kilometers (92.2 million miles); light travel time: 7 minutes, 13 seconds



Currently en route to the asteroid Ceres, where it will arrive in February 2015.

Time since launch: 2473 days
Time since Vesta departure: 668 days
Current distance from Ceres: 8.2 million kilometers (5.1 million miles)
Current distance from Earth: 371 million kilometers (231 million miles); light travel time: 20 minutes 37 seconds



Currently en route to Jupiter, where it will arrive in August 2016.

Time since launch: 1073 days
Current distance from Jupiter: 337 million kilometers (209 million miles)
Current distance from Earth: 630 million kilometers (391 million miles); light travel time: 34 minutes, 57 seconds


Voyager 1

Time since launch: 13,466 days
Current distance from Earth: 19.1 billion kilometers (11.88 billion miles); light travel time: 17 hours, 43 minutes


Voyager 2

Time since launch: 13,468 days
Current distance from Earth: 15.63 billion kilometers (9.72 billion miles); light travel time: 14 hours, 29 minutes

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About The Author
Justin Cowart
Justin Cowart is a geologist interested in Earth and Solar System history. As a geologist, he spends hist time looking at the ground, but in his free time he looks to the skies as an amateur astronomer.

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