The Beagle has landed...

Posted: May 28, 2003

Well, not quite but the innovative Beagle 2 will soon be on its way to Mars aboard ESA's Mars Express. Once at the Red Planet, it may turn up evidence of past or present life.

The Beagle 2 lander is carried to the Red Planet aboard the Mars Express spacecraft, as shown in this mission illustration. Credit: Astrium
Mars is under attack. Over the coming months, no less than five spacecraft are due to land on or orbit around the Red Planet. And the good news for UK space enthusiasts is that one of them is British. It's called Beagle 2 -- after HMS Beagle, the ship that carried Charles Darwin on the historic voyage which led him to write On the Origin of Species. Although UK science instruments have been flown into space before, this is the first time Britain has led an entire deep space mission.

Beagle is a lander and holds the record for being the smallest lander ever to be sent to Mars. It has the highest payload fraction of any other Mars lander, with nearly 9 kilos of its 32.7-kilo landed mass devoted to science instruments. Ambitiously it's going to look for evidence of past or present life on Mars. The last probes to attempt that were the twin Viking landers, in the late 1970s, but their findings indicated that Mars is a sterile, lifeless world. Then, in 1996, came the announcement by NASA of what looked like fossilized bacteria found inside a Martian rock. Suddenly, all eyes were back on the Red Planet.

The Beagle 2 lander with its parachutes and gas bag systems are packaged in the entry probe. Credit: Astrium
The Beagle concept was conceived in 1997, by Professor Colin Pillinger, at the Open University, in Milton Keynes. The European Space Agency (ESA) had announced its Mars Express spacecraft, but, as things stood, it was just an orbiter mission.

"Colin forced his way into an ESA meeting on Mars Express and told them they were crazy going to Mars without a lander," says Sims. In March that year, Pillinger called a meeting at the Royal Society in London, at which he laid down the challenge to the UK and Europe to design and build a lander for Mars. A three-day workshop followed at the University of Leicester, to develop ideas.

A design and experiment package was put to the ESA Science Programme Committee during late 1998. ESA gave final approval for Beagle 2 on November 10, 1999.

If all goes to plan, Beagle will arrive on the surface of the Red Planet on December 25 this year.

Beagle 2 plunges into the Martian atmosphere. Credit: ESA/Medialab
The landing site, the Isidis Basin near the Martian equator, was chosen for a number of reasons. Near the equator, the environment on Mars is at its warmest, requiring minimum thermal protection, reducing the weight of the craft. Because Isidis lies below the Martian 'sea level', there is a deeper atmosphere between space and the ground, giving Beagle's parachutes more time to slow the craft's descent.

"We've also been careful to pick a place where we think there's been water in the past," says Sims. "But which is flat enough and doesn't have too many rocks, so it's safe to land on."

Bumpy landing
The craft will land using a cluster of airbags, similar to the system that successfully deployed Mars Pathfinder in 1997. Beagle will hit the Martian atmosphere at Mach 31.5 (over 14,000 mph). Initial braking is by air resistance using a protective heat shield.

Once slowed sufficently, a drogue parachute opens and the heat shield is jettisoned by pyrotechnic bolts. The main parachute is then deployed. Two hundred meters above the surface, as measured by a radar altimeter, the airbags inflate, and on first contact with the ground the parachute is released, allowing the lander to bounce away.

An artist's impression of Beagle 2 moments after landing on Isidis Planitia. Credit: ESA/Medialab
Once it comes to rest, a tie is cut, the bags roll away and Beagle drops onto the surface. Software hinge mechanism which clamshell and unfurls Beagle's array of solar panels so that the science mission can begin.

Paw prints
Original designs for Beagle included a small tethered rover which could roam around in the vicinity of the landing site, gathering rock and soil samples. "Mass constraints crept in and later forced us to drop that," says Sims. "But we still had to have some kind of deployable instrument capability, so we went for a small robotic arm. On the end is a collection of instruments called the PAW -- position-adjustable workbench."

The robot arm can reach a surface area of about one square meter. Scientists hope there will be some interesting rocks within that range. "If you go on the Viking and Pathfinder data, then there should be three to four 10-centimeter-size rocks within that one square meter," says Sims.

A mock-up of the Beagle 2 lander and its arm. Credit: Astrium
The instruments on the arm's PAW include a rock corer-grinder, for burring away the surface eroded layers of rocks and extracting samples. There's a stereo camera for photographing the landscape and navigating the arm. A microscope has filters for red, green, blue and ultraviolet light -- the latter was included because organic material fluoresces under UV. A wind sensor on the arm allows Beagle to look for variations in wind speed with height, and there's an X-ray spectrometer and a gamma-ray Mossbauer spectrometer.

"The idea is that with the X-ray spectrometer you measure the chemical composition of the rocks," says Sims. "If the chemistry looks right, you look at the mineralogy with the microscope, which gives you the structures, and with the Mossbauer, which tells you how oxidized the rocks are."

Mars looks red because much of the iron on its surface is oxidized -- it's basically rusty. "Oxides destroy organic matter," explains Sims. "So if you're looking for life, ideally you want to pick a rock that isn't too highly oxidized. If that's the case, you cut a core with the corer-grinder and drop it into the gas analysis package in the lander's base."

This instrument, designed by Pillinger's team at the Open University, looks for the key signature of life, which if it's there, will lie in the sample's carbon chemistry. There are two stable isotopes of carbon, one with 12 neutrons in its atomic nucleus and one with 13. Biology prefers carbon-12.

Professor Colin Pillinger and Beagle 2 model. Credit: All Rights Reserved Beagle 2
The gas analysis package looks for an excess carbon-12 by burning the samples in oxygen. This converts any carbon present into carbon dioxide (CO2). A device called a mass spectrometer then separates out the CO2 made with carbon-12 from the heavier CO2 that's made with carbon-13, and measures their relative abundances.

Biologically produced compounds burn at a lower temperature than those that are produced geologically, so the gas analysis package measures the carbon-12 to carbon-13 ratio as the burning temperature is steadily increased. An excess of carbon-12 at low temperature is then a strong indicator of past or present life. "That isotopic signature is preserved over billions of years," says Sims.

The PAW also carries Beagle's mole, a self-burying drill that will be used to probe the Martian subsurface. It's propelled by a compressed spring and drive mass, which can knock the mole across the surface at a rate of one centimeter every six seconds, or hammer it into the soil a millimeter at a time. The mole can reach depths of up to two meters. Tethered, it is recoverable with a winch. A cavity in the tip of the mole can open to grab soil samples, which can then be dropped into the gas analysis package. The gas package will also be used to check for atmospheric methane, which if detected, may also be biological in origin.

Beagle has been thoroughly sterilized prior to its departure; to prevent Earthly bugs contaminating the biology experiments and to prevent terrestrial bacteria settling on Mars. "There's a UN treaty obligation not to wantonly contaminate other planets," explains Sims.

In the air
A further array of environmental instruments is stowed in the lander base including sensors to monitor radiation, dust and atmospheric oxides. The findings of an ultraviolet sensor, the first to be landed on Mars, could be especially relevant to Martian biology, since UV light can be harmful to organic compounds.

The suite will run for Beagle's entire 180-Martian-day primary mission, charting the evolution of the planet's atmosphere through the seasons. An extended mission is possible, taking Beagle 2's active stay on the surface to 669 days, or one Martian year -- assuming the lander survives. Even if Beagle's experiments don't detect any biological signatures, life may still be lurking elsewhere. "The problem is that Mars is a big planet," says Sims. "Its surface area is equivalent to the surface land area of the Earth." In its search for life, Beagle will have made a full geochemical characterization of its landing site, adding enormously to our limited knowledge of the planet's surface.

The Beagle 2 lander, to be carried on ESA's Mars Express, is equipped with a suite of instruments designed to look for evidence of life on Mars. Credit: All Rights Reserved Beagle 2
Other Mars scientists agree that Beagle is a noble venture. "Beagle 2 is innovative, sound and attractive," says Dr. Jim Garvin, NASA's lead scientist for Mars Exploration at NASA Headquarters, Washington. "Any approach for reaching the surface of Mars, for exploring its various nuances, vagaries and exciting elements in novel new ways and from new vantage points is a great thing."

NASA is currently selecting concepts for its Mars Scout missions, due for launch in 2007. "Amongst these are several small landed laboratory approaches that are similar in scientific thinking to the Beagle 2," says Garvin. Sims adds that he believes much of the technology and instrumentation concepts developed for Beagle will be carried forward into ESA's Aurora Programme of planetary missions.

So even if Beagle 2 fails to find evidence for life on Mars, the innovative concepts behind the mission look set to stay. On the other hand, if the mission is a success, it could help scientists write some of the most significant chapters yet in planetary science and evolutionary biology. Darwin would be proud.

A cast of thousands
The main partners in Beagle 2 are: The Open University, Astrium, the University of Leicester, the British National Space Centre and ESA.

All of Beagle's instruments, except for the Mossbauer spectrometer, were developed by international consortia. The microscope was developed by a team led by the Max Planck Institute for Aeronomy in Lindau. The stereo cameras come from a consortium organised by the UK's Mullard Space Science Laboratory. Development of the X-ray spectrometer was headed by the University of Leicester. Development of the mole was led by DLR in Germany, with considerable Russian input. The corer-grinder was developed principally by Hong Kong Polytechnic. The Mossbauer spectrometer comes entirely from the University of Mainz. And the gas analysis package comes from the Open University, with some electronics provided by Astrium.

The major software contributions came from Logica, who developed the entry and descent software, and SciSys, who are responsible for the landing software.

Dr. Paul Parsons is a freelance science writer and Astronomy Now's news editor.

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