Chaos in the Canyon

Ophir Chasm
Perspective view. Ophir Chasm in the northern Marineris Valley network.
Credit: ESA/Mars Express

These images, taken by the High Resolution Stereo Camera (HRSC) on board ESA’s Mars Express spacecraft, show the Ophir Chasma, a northern part of the Valles Marineris canyon.

Although the region has been mapped in detail during several missions, many secrets of the geological history of Valles Marineris still remain a mystery. Valles Marineris is a huge canyon system around 4000 kilometers (2400 miles) long, up to 240 kilometers wide (144 miles) and up to 6.5 kilometers deep (3.8 miles). Its connected ‘chasma’ or valleys may have formed from a combination of erosion and tectonic activity. The floor of the canyon shows morphological evidence of volcanic, fluvial or even glacial activity.

The northern scarp of Ophir Chasma, towards the left in these images, has an elevation of up to 5000 meters (3 miles). Several slopes of collapsed material, indicating slope instabilities, can be seen at the base of the scarp and can be traced southwards along the valley floor for more than 70 kilometers (42 miles).

Ophir Chasm
Perspective view. Ophir Chasm in northern Marineris Valley network.
Credit: ESA/Mars Express

In the south, east of the rounded and apparently smooth Baetis Mensa ridge, the dark chaotic terrain of Candor Chaos can be seen. This terrain is characterised by polygonal blocks that suggest material movements in north-south and east-west directions. Chaotic terrain on Mars is often connected to outflow channels, indicating the catastrophic release of large subsurface water reservoirs, and the subsequent collapse of tye above-lying rock.

On 22 August, Mars Express entered into a solar conjunction phase, and on 15 September the craft approached to within one degree away from the Sun as viewed from Earth. Mars Express itself was in no danger as it was in fact safely voyaging around Mars 399 million kilometers (240 million miles) away from Earth on the opposite side of the Sun. For mission controllers, a solar conjunction means that a spacecraft, the Sun and Earth are in alignment. Yesterday, engineers successfully woke up ESA’s Mars Express from a lengthy and long-planned ‘nap’ as it travelled out of a conjunction, avoiding potential communications interference from the Sun.

If you use a mobile phone, you have probably experienced static when a building or surrounding geography interferes with the signal between your handset and the receiving antenna.

Ophir Chasm
Perspective view. Ophir Chasm in northern Marineris Valley network. Credit: ESA/Mars Express

During the recent conjunction, communications with Mars Express could similarly have been affected, but the interference, caused by the Sun’s corona, was potentially more serious than just a dropped call. The solar conjunction, however, meant that radio command signals travelling to and from Mars Express passed through the Sun’s super-heated, super-active corona, which comprises the upper reaches of the Sun’s atmosphere. This highly active area is a hotbed of strong electromagnetic radiation as well as a source of the intense particles that form the solar wind.

Had mission controllers attempted to transmit radio signals to Mars Express as the Earth-to-spacecraft line of sight skimmed by the Sun, chances are high that the signals would have been degraded or scrambled by interference from the corona. Commands might not get through (or only partially so) with unpredictable effects on the spacecraft’s operation.

To cater for this event, flight controllers at the European Space Operations Centre (ESOC) in Darmstadt, Germany, had long planned for a ‘blackout’ period lasting from 22 August until 27 September in which Mars Express was placed in a minimum activity configuration with no science data being downloaded and only the barest of command signals being sent up.

Ophir Chasm
Perspective view. Ophir Chasm in northern Marineris Valley network.
Credit: ESA/Mars Express

"We had a one week preparation period going into blackout and the same to come out, with three weeks of ‘stay still’ in between," said Mars Express Spacecraft Operations Manager Michel Denis, adding, "We wanted the spacecraft to be as stable and quiet as possible."

Denis said that communications were not totally blocked during the conjunction. This allowed controllers to monitor the status of the spacecraft and in fact to collect and analyse samples of radio signals received from Mars Express that were distorted by the solar corona precisely what radio astronomers do when they study solar activity. In space science, somebody’s noise is always somebody else’s signal.

During the Mars Express quiet period, ESOC engineers maintained a 300-bit-per-second (bps) downlink channel open for daily, if highly limited, communication. This was just a trickle, however, compared to the usual 30- to 200-kilobit-per-second (kbps) science data downlink. The spacecraft was, for most intents and purposes, left undisturbed. Yesterday, controllers on Denis’s team received full signal from the spacecraft for the first time in over a month, and re-established a full daily routine of spacecraft communications, including transmitting signals in both the X- and S-bands.

Satellites generally use the S-band (2.0-2.3 GHz) for uplink telemetry and telecommanding while the X-band (10.7-20 GHz) is used for low-power, high-volume data transmission back to Earth. To achieve this, engineers have been working since last week to reload scientific experimentation programs into on-board processors, verify communications and generally make sure that Mars Express is once again wide awake and ready for scientific exploration.

Recent Mars Express milestones

  • Discovery that Martian atmospheric water vapour and methane seem to have a common underground source: 20 September 2004
  • Date of maximum distance from Earth: 5 September 2004 (399,003,610 kilometers)
  • Radio-signal travel time at this distance: 22.2 minutes
  • Date of last autonomous switch to ‘Safe Mode’: 15 March 2004

Mars Express’s orbiter will operate for a whole Martian year (687 Earth days). It is expected that the mission will be extended by another Martian year. After the mission, the Mars Express orbiter will simply keep orbiting the planet for at least 50 years.

Related Web Pages

Great Terraforming Debate: Part I
Great Terraforming Debate: Part II
Great Terraforming Debate: Part III
Great Terraforming Debate: Part IV
Great Terraforming Debate: Part V
Great Terraforming Debate: Part VI
Great Terraforming Debate: Part VII
Mars Exploration Rover Mission: Home
NASA Mars Exploration Program