NASA Mars probes watch comet near-miss

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All three of NASA's orbiters were moved to the far side of Mars to protect them from comet debris (Image: NASA)

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After a dramatic, one-in-a-million-years close encounter between Mars and comet Siding Spring on Sunday, all five functioning US Mars probes survived and are reportedly healthy. NASA confirms that the Mars Odyssey, Mars Reconnaissance Orbiter (MRO), and the Mars Atmosphere and Volatile Evolution (MAVEN) orbiter, along with the rovers Curiosity and Opportunity came through without a scratch and are returning valuable data on the comet.

According to NASA, C/2013 A1 Siding Spring is a newcomer to the inner Solar System as it makes its first ever visit from the Oort Cloud that lies on the outer fringes of the system. Discovered in 2013 by Australia’s Siding Spring Observatory, its trajectory was calculated to take it so close to Mars this year that astronomers at one time feared that it might impact the Red Planet. However, as it drew closer, more precise observations showed that it would only come within a cosmic hair’s breadth.

On October 19 at 11:27 am PDT, Siding Spring reached its closest point to Mars, passing within a mere 87,000 mi (139,500 km) of the planet. For comparison, that distance is about a third of the distance between the Earth and the Moon. NASA’s orbiting probes were in no danger of colliding with the comet, but with it traveling at a speed of approximately 125,000 mph (56 km/sec), the dust from its tail that reached Mars 100 minutes after the encounter posed a threat like a blast of shrapnel. To avoid this, NASA ordered the probes to carry out an orbital maneuver that placed Mars between them and the comet during the danger period.

NASA reports that during the encounter all but one orbiter maintained communications, and all were able to carry out observations that may provide scientists with a unique glimpse into what the Solar System was like four billion years ago.

Mars Reconnaissance Orbiter

The workhorse NASA’s trio of orbiters, the
MRO came through the encounter with all computers and subsystems working normally and uploading 1.5 megabits per second with NASA's Deep Space Network.

The space agency says that the MRO watched the comet go by with its High Resolution Imaging Science Experiment (HiRISE), the Compact Imaging Spectrometer for Mars (CRISM), and the Context Camera (CTX), and will continue to observe the comet while it remains within range over the next few days.

Meanwhile, the MRO’s Mars Climate Sounder (MCS), the Mars Color Imager (MARCI) and the Mars Shallow Radar (SHARAD) will record the effects of the comet’s dust tail on the atmosphere.

MAVEN

NASA's newest orbiter at Mars,
MAVEN has been on station for only a month, having arrived on September 21, and is still undergoing its commissioning phase during which it’s been calibrating its instruments. During the protective phase of the comet encounter, its main antenna was not pointed toward Earth, so a secondary, low-speed data link was employed.

MAVEN’s instruments sent back data on the gases and dust released by Siding Spring, while others are currently assessing the impact of the comet’s tail on the Martian atmosphere.

Mars Odyssey

The longest-lived unmanned probe ever sent to the Red Planet,
Mars Odyssey was the only one of the three orbiters to go out of communications with Earth, but later telemetry indicated that the orbiter is still in good health. It observed Siding Spring, using its Thermal Emission Imaging System (THEMIS) to record images of the comet, while its High Energy Neutron detector looked at possible effects on the atmosphere.

The data from these instruments will be downloaded and processed at mission control over the next few days.

Siding Spring as seen by Opportunity (Image: NASA/JPL-Caltech/Cornell University/ASU/TAMU)

Curiosity and Opportunity

Meanwhile, NASA’s two surface rovers,
Opportunity, made observations of their own, with Curiosity using its imaging camera to record the comet’s passage and Opportunity snapping panoramic pictures in what may have been a front row seat at the best show in the Solar System.

The video below outlines the role of the various probes during the Mars/Siding Spring encounter.

Source: NASA

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