by Ben Bova
Scientists sometimes morosely joke that it takes longer to get a spacecraft mission through Washington’s maze of politics and bureaucracies than it does to fly the spacecraft to another planet.
Make no mistake about it: Politicians make their decisions for politi-cal reasons, not scientific. The first question a politician asks when faced with a decision is, “How will this affect my chances for reelection?” Astrobiology has no powerful lobbyists to support it in the corridors of Washington politics. Indeed, there are powerful interests who fear what the astrobiologists might find; they have already moved to block SETI, and they could work against the goals and hopes of astrobiology in the future.
Those goals are nothing less than the answers to these questions:
Is there life on Mars now, or was there once life on the red planet that is now extinct?
Does life exist beneath the ice of Jupiter’s frozen moons? Does life exist beneath Jupiter’s swirling clouds?
Where else in the solar system might we find living organisms or the fossils of creatures that were once alive?
Did life truly arise on Earth out of nonliving chemicals or was our planet “seeded” by organic matter brought in by asteroids and comets?
Are there other intelligent species in the Milky Way galaxy? Or in the wider universe of other galaxies?
Will human beings be able to live in space or on other worlds?
Astrobiologists are seeking the answers to these puzzles. How? By searching for evidence. Science is a hunt that depends on observation and measurement. Here is an agenda for action. We will start by listing programs that are already underway or in the planning stages. Then we will look at what can be done, and what should be done, to find the answers that the astrobiologists seek.
WHAT IS PLANNED FOR MARS
Since 1965, when Mariner 4 flew past Mars and sent back twenty-two photographs, robotic spacecraft have told us more about the red planet than all the Earthbound observations since Galileo’s time. The most recent spacecraft mission is NASA’s Mars Odyssey, which began a two-year mapping mission when it established itself in a close orbit around Mars early in 2002. Mars Odyssey detected evidence for frozen water below the surface of the planet’s polar regions, regions of permafrost as large in area as the continental United States. Water ice has also been seen on the surface near the south pole. In addition, the spacecraft is making measurements of the planet’s atmosphere and radiation environment.
The United States and other nations plan to send robotic missions to Mars every two years, when Mars is closest to Earth. In 2003, when Mars came closer to Earth than any time in the previous 60,000 years, a trio of exploratory spacecraft were launched toward the red planet.
In June and July 2003, NASA launched a pair of Mars Exploration Rovers (MERs), which will land on the planet early in 2004 and, like the earlier Sojourner, trundle across the red sands of Mars under remote control from its operators at the Jet Propulsion Laboratory in California. Each rover carries nine cameras, two spectrometers, and equipment for digging into the Martian regolith and grinding soil and rock samples. While the rovers will be able to dig only about a half-centimeter into the ground, scientists expect to study the exposed rock surfaces with the rovers’ other instruments. The MERs will perform geological studies, basically; they were not designed for biological research.
MER-A will land at the 166-kilometer-wide Gusev Crater, while MER-B will touch down in Meridiani Planum, not far from the Ares Vallis region where the Pathfinder/Sojourner spacecraft landed in 1997. Both sites appear to have harbored surface water in Mars’ past.
The European Space Agency’s Mars Express was also launched in June 2003, from the Russian space center at Baikonur, in Kazakhstan. It is scheduled to arrive on the red planet in December 2003. Mars Express will search for underground water from a polar orbit using a radar system developed with the Italian space agency.
Mars Express will also carry Great Britain’s Beagle 2 lander. The small lander, named after the ship on which Charles Darwin served as a naturalist in 1831, will land at Isidis Planitia, the third largest impact basin on Mars, where it will bore into rocks and take soil samples, searching for the presence of water and carbon-based organic molecules.
Japan’s Nozomi (meaning “Hope”) was launched in 1998 into a long low-power trajectory designed to loop around the Earth and the Moon before gaining enough velocity to head for Mars. The first swing-by of Earth failed, however, and the spacecraft was sent into a trajectory that looped around the Sun, where a solar flare knocked out a heater needed to warm the fuel the spacecraft needs to slow down enough when it reaches Mars to take up an orbit around the planet.
In June 2003 Nozomi successfully accomplished a second swing around Earth and slingshotted at last toward its rendezvous with Mars. Engineers are working to fix the ailing heater before the spacecraft reaches Mars in December 2003.
The Mars Reconnaissance Orbiter is intended to examine the Martian surface in unprecedented detail, sending back imagery of 20- to 30-centimeter resolution, clear enough to resolve rocks the size of beach balls. NASA plans to launch Mars Reconnaissance Orbiter in 2005.
Politics always determines what the scientists and engineers can accomplish. France had planned to send a mission to Mars called NetLander in 2007 to study the red planet’s weather and subsurface geology. NASA was one of several contributors to the international mission. However, budget cuts at the French space agency, CNES, shook the $350 million project. Then, early in 2003, NASA announced that it was pulling out of the NetLander project, claiming that the risks of “piggybacking” the spacecraft on one of its planned Mars missions were too great.
France canceled NetLander altogether. Observers on both sides of the Atlantic wondered if the acrimony between the U.S. and French governments over Iraq and other political issues had caused NASA’s retreat from the program and thereby forced its cancellation.
Possibly as early as 2007, NASA hopes to launch a highly sophisticated roving vehicle that will be a long-range, long-duration mobile laboratory.
The space agency also wants to send smaller Scout missions to Mars; each mission would be selected from proposals made by independent scientists and might include soaring airplanes or long-range balloons equipped with sensors to study the atmosphere and surface.
After 2010, NASA intends to send sample-return missions to Mars. These will bring samples of Martian rock and soil back to laboratories on Earth.
All of these missions are subject to funding decisions by their governments. Except for the spacecraft already on their way to Mars, any of them could be cut back, stretched out, or canceled altogether. None of them, to date, include equipment to drill deeply enough into Mars’ crust to search for a deep, hot biosphere.
Nor are there any plans for human exploration of Mars, although it is tacitly assumed that if the robotic probes find enough encouraging evidence, human expeditions will eventually be mounted.
WHAT IS NEEDED FOR MARS
The current plans for sending robotic probes to Mars are an incremental approach. Constrained by budget strictures and politics, the astrobiologists hope to glean more and more information about Mars, little by little. It is extremely doubtful that any of the probes now in the planning stages will (if they actually get off the ground) be able to find unequivocal proof of Martian life, either fossils or living organisms. Instead, the astrobiologists hope that each mission will provide enough new information to allow them to send the next mission, constantly gaining more data, more understanding.
Eventually, they will reach a critical juncture. The robotic probes will have accomplished as much as can be expected of them. To learn more about Mars, to find decisive evidence for life on the red planet (or its absence), it will be necessary to send human scientists to Mars.
Human exploration of Mars is deemed to be so much more expensive than robotic probes that there are no existing plans for sending people to Mars. The astrobiologists hope that the robotic probes w
ill amass enough positive evidence eventually to convince the taxpaying public and their representatives in Washington to mount a scientific expedition to the red planet.
Must human missions to Mars be so costly? Not necessarily. A major factor in the cost of human expeditions is the cost of bringing the people back to Earth again. This means that the spacecraft must carry all the supplies needed to sustain the human crew to their objectives on Mars and then back to Earth again.
Space engineers such as Robert Zubrin have shown that these costs could be cut enormously by sending equipment to Mars that can produce out of the local Martian soil and air the oxygen and water needed for life support and the propellants needed for the return flight to Earth. By “living off the land,” Zubrin—and other space enthusiasts—believe human expeditions to Mars could become little more expensive than missions such as the 1976 Viking or the present Cassini/Huygens mission to Saturn’s moon Titan. Certainly the first human expedition to Mars will cost at least a few billion dollars, but if Zubrin’s type of plan is put into effect, human beings could study the rock-strewn, rust-red sands of Mars for far less than the $20 billion cost (1960s dollars) of the Apollo program.
And the results could be priceless.
When robotic probes begin to send samples of Martian rocks and soil back to Earth, the problems of back contamination will become paramount. The International Space Station could be used as an isolation ward, where Martian samples could be studied before being allowed to reach Earth. Perhaps a special module could be added to the ISS, not even attached to the rest of the station but flying freely alongside it, for such work. When astronauts return from Mars, the orbital isolation ward could be used to check them out before they set foot back on Earth.
Moreover, modules could be attached to the space station to serve as training centers for Mars-bound astronauts. They could live and work for months in microgravity, if necessary, before they start off for the red planet.
THE MOON
No one expects to find living organisms on the Moon, except for the Earth-born bacteria or viruses that hitch rides on spacecraft. Thomas Gold, originator of the deep, hot biosphere concept, maintains that life could have existed under the lunar surface while the Moon’s interior was still hot. Deep drilling may bring up fossilized bacteria-like forms.
The Moon could be an excellent platform for astronomy and especially for SETI. Its airless surface offers a vacuum that is 10,000 times rarer than the vacuum of near-Earth orbital space, where the Hubble and other space observatories now orbit. Moreover, the Moon’s surface contains abundant raw materials such as silicon and aluminum that can be used to construct giant telescopes without the cost of hauling the construction materials up from Earth’s surface.
The lunar farside could be the best place in the solar system for very sensitive SETI radio searches. The farside is always turned away from Earth, and therefore it is insulated from Earth’s background radio chatter by nearly 3,500 kilometers of rock. When the Sun is down, during the two-week-long night on the farside, there is no quieter radio environment in the solar system. Enormous arrays of radio telescopes could be built in the Moon’s light gravity out of local raw materials. If radio SETI is ever to succeed, it might very well be from an observatory on the lunar farside.
However, NASA has no plans at all for any future missions to the Moon. Japan has launched an automated lunar probe, but otherwise the Moon is not on any government’s agenda for future missions.
Private organizations, however, are aiming for the Moon. TransOrbital, Inc., of Alexandria, Virginia, has designed TrailBlazer, the first commercial lunar probe, and plans to launch it to the Moon aboard a Russian Dnepr booster. TrailBlazer will spend a month in lunar orbit, sending high resolution video imagery back to Earth. TransOrbital had to obtain permission from the U.S. government for this mission, a move that prompted critics to decry Washington’s willingness to allow private enterprise to begin the “commercial development” of the Moon.
EUROPA
There may well be an ocean of liquid water beneath the thick ice mantle of Jupiter’s moon Europa (and possibly Ganymede and Callisto, as well). NASA’s Jet Propulsion Laboratory was planning to launch Europa Orbiter in November 2003 into a trajectory that would have allowed the spacecraft to enter orbit around Jupiter in August 2006. Once there, the spacecraft would have made observations of the planet itself, as well as undertaken a number of close flybys of Ganymede. After that, the spacecraft was to settle into an orbit around Europa.
Those plans were dashed early in 2002, when NASA canceled the Europa mission (and the mission to Pluto, as well).
What is needed, however, is not an orbiter but a spacecraft that can land on Europa’s ice-covered surface and take samples of the ice and any organic material in it.
Operating equipment on Europa by remote control from Earth will be difficult, if not impossible. The problem is distance. At its closest approach to Earth, it still takes more than half an hour for a communications signal to cross the 625-million-kilometer distance between the two planets. It might be necessary to have a team of human directors much closer to the site. If that turns out to be the case, it will be wiser to plan for human expeditions to Europa from the outset. The radiation environment is intense: Jupiter’s mammoth Van Allen Belt drenches all the Galilean moons with lethal levels of ionizing radiation.
The alternative to human missions to Europa or anywhere else in the Jovian system is to send preprogrammed robotic vehicles that can carry out the activities planned for them before they left Earth but cannot adjust their programming (in less than half an hour) to take advantage of new situations.
TITAN
Seventeen nations contributed to the Cassini/Huygens double spacecraft, which is scheduled to reach Saturn in June 2004 after a seven-year flight that saw the craft swing past Venus twice, once past the Earth, and once past Jupiter, gaining speed from the gravity boosts provided by each planet.
Because of a flaw that developed in the spacecraft’s communications software, the Cassini spacecraft will orbit around Saturn three times before releasing the Huygens probe to drop into the thick, cold atmosphere of Titan.
While Cassini studies Saturn and its elaborate retinue of rings, Huygens is intended to land on Titan’s surface and transmit data for as long as ninety minutes. This, of course, is merely a first reconnaissance of Titan. The data returned from Huygens will be used to plan future missions. The astrobiologists are particularly interested in the organic chemicals that make up Titan’s smoggy atmosphere. Are there really lakes of petroleum-type liquids on Titan’s surface? Is there life in them?
OTHER PLANETS OF THE SOLAR SYSTEM
Despite funding problems, the European Space Agency approved its Venus Express program for a launch in 2005. The program’s fate was in doubt because member-nation Italy was unable to fund a key sensor for the spacecraft, VIRTIS (Visible and Infrared Thermal Imaging Spectrometer). Developed at the Institute for Space Astrophysics in Rome, VIRTIS is designed to detect the low levels of infrared radiation that get through Venus’ perpetual blanket of clouds and thereby allow scientists to study the composition of the planet’s lower atmosphere, beneath the clouds. ESA, which consists of fifteen member nations, agreed to cover the costs of the sensor’s development so that the mission to Venus can go forward.
Venus Express will also study the planet’s magnetic field and geology. No other spacecraft are scheduled for Venus until 2009, when Japan intends to launch its Planet C mission.
As we have seen, a mission to Pluto was inserted into the NASA budget for fiscal year 2002 by Congress, killed early in calendar year 2002, and then reinstated under the New Horizons program. Except for the Cassini/Huygens spacecraft already on its way to Saturn, NASA now has no other plans for future missions to the planets beyond Mars.
NASA plans probes to Mercury and Venus, but again these are in the paperwork stage and must run the gauntlet of budgetary priorities.
COMETS AND ASTE
ROIDS
Other missions are aimed at comets and asteroids. The Deep Space 1 probe photographed Comet Borrelly in 2001, for example, and the NEAR-Shoemaker spacecraft landed on the asteroid Eros in that same year. As we have seen, NASA’s Contour spacecraft was destroyed in flight before reaching its first objective, Comet Encke. Stardust, launched in 1999, will take samples from the tail of Comet Wild 2 in January 2004. Deep Impact will be launched that month, heading for Comet Tempel 1. In July 2005, Deep Impact will fire a 400-kilogram missile into the comet’s icy head and observe the material ejected from it by the explosion.
The most ambitious spacecraft mission is ESA’s Rosetta, which was to be launched early in 2003 on an Ariane-5 booster from the ESA launch center in Kourou, French Guiana. Rosetta was intended to spiral outward past Mars and fly by the asteroid Otawara in July 2006, then the asteroid Siwa in July 2008. In July 2012, it would have touched down on the surface of Comet Wirtanen, near the orbit of Jupiter, some 650 million kilometers from Earth. However, the Ariane-5 heavy-lift booster failed on its first flight, and in January 2003 the Rosetta mission was postponed for at least one year, scrambling the intended rendezvous with Wirtanen and the asteroid flybys as well. Further budget reductions and financial crises in the European Space Agency have thrown Rosetta’s future funding into a political quagmire.
Meanwhile, in May 2003, Japan’s Institute of Space and Astronautical Science (ISAS) started a mission that is intended to return a sample of an asteroid to Earth. Launched from ISAS’s Uchinoura space center in Kyushu, the Muses-C spacecraft is headed for asteroid 1998SF36, some 300 million kilometers from Earth. Propelled by a high-efficiency solar-powered ion engine, the 510-kilogram spacecraft will land on the asteroid and scoop up a gram of surface material (mostly dust, undoubtedly) and send it back to Earth in a special return capsule that will parachute to a landing in Australia in 2007.