For the very first time in human history, a human voice was streamed from the surface of another planet and traveled some 168 million miles (267 million km) into space before it was heard on Earth. The audio was a pre-recorded message from NASA administrator Charles Bolden, who sent a congratulatory message to the engineers involved in the US$2.5 billion mission to safely land the Mars Science Laboratory – better known as the Curiosity rover – on the surface of Mars.
The 500 kilobyte audio file was streamed back to Earth as part of a communications test. This marks the first time we've heard a human voice beamed from the surface of an alien planet. It's a small step toward extending human presence to other planets, and has been sent with the hope that, in the not-too-distant future, generations that are hearing it today will be the very same who land the first humans on the surface of the Red Planet.
One of the challenges of a landed mission is to transmit data from Mars to Earth. Curiosity has very limited transmission capabilities on the direct Mars to Earth path: its antenna dish is a single foot (30.5 cm) in diameter, and with a measly power of 15W at its disposal it could only achieve data rates of around one kilobit per second without external help.
Fortunately, however, the rover gets help from three Mars orbiters that act as a relay and increase the data rates considerably. On landing day, Odyssey, the Mars Reconnaissance Orbiter (MRO) and Mars Express spacecraft were all positioned optimally to relay data and make sure that the entry and descent stage proceeded without hiccups. Ever since, MRO and Mars Express have been collecting and relaying data from and to the rover, bumping data transfer rates up to about two megabits per second, while the European Mars Express is serving the role of a backup should either of NASA's incur into problems.
Odyssey and MRO are in orbit around Mars at an altitude of 185 to 250 miles (300 to 400 kilometers) and, whenever they appear over Curiosity’s horizon, they offer radio contact with the rover for ten to fifteen minutes at a time. The connection speed improves the higher the orbiter is over Curiosity’s head, and NASA’s newly developed algorithms for adaptive data rates are maximizing the amount of data that can be beamed back to Earth on any given day.
This new approach to achieve optimal data rates has been very fruitful. Taken together, MRO and Odyssey have already relayed close to one gigabyte of data since the rover’s landing. That’s almost three times more than the Spirit, Opportunity, or Phoenix missions had achieved in the same amount of time.
The voice playback was released to the media along with new telephoto images taken by the 100-mm lens and the 34-mm wide angle lens of Curiosity's Mast Camera (Mastcam) instrument. The high resolution images of the lower slope of the nearby Mount Sharp show eroded knobs and gulches with clearly visible geological layering.
"This is an area on Mount Sharp where Curiosity will go," said Mastcam principal investigator Michael Malin, of Malin Space Science Systems in San Diego. "Those layers are our ultimate objective. The dark dune field is between us and those layers. In front of the dark sand you see redder sand, with a different composition suggested by its different color. The rocks in the foreground show diversity -- some rounded, some angular, with different histories. This is a very rich geological site to look at and eventually to drive through."
As part of the preliminary checks before Curiosity drives away toward Mount Sharp, NASA engineers conducted a test in which the SAM (Sample Analysis at Mars) instrument took a brief sniff of Mars’s atmosphere. SAM’s mass and tunable laser spectrometers were used to look for the major constituents of the Martian atmosphere.
Here, there was a minor hiccup: as it turns out, an excessive amount of residual Earth atmosphere and calibration gas leaked into the tunable laser spectrometer. As a result, the very first measurement registered unexpectedly high levels of methane, and caused quite a stir among NASA engineers – at least until they figured out that what they just measured wasn’t Mars’s atmosphere, but rather Florida’s. The unwanted gases have now been flushed from the system and the instruments are performing as expected.
This minor incident aside, these preliminary tests were a complete success. With all of the relevant instruments properly calibrated, Curiosity will be able to take a first, proper look at the composition of the atmosphere on Mars. Over the coming months, comparing those results to a similar analysis of local rocks that formed billions of years ago might give us a better insight into Mars’s distant past.
Curiosity is currently investigating the scour marks left by the thrusters of its powered descent stage, which have uncovered bare rock. The DAN instrument, which is designed to look for subsurface water, and ChemCam are gathering information on the nature of the soil around it.
Then, in just a few days’ time, the rover will start heading east to discover new lands and landscapes on the Martian surface.
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