Space and Beyond

A tale of planetary woe

Once upon a time − roughly four billion years ago − Mars was warm and wet, much like Earth. Liquid water flowed on the Martian surface in long rivers that emptied into shallow seas. A thick atmosphere blanketed the planet and kept it warm. Living microbes might have arisen, some scientists believe, starting Mars down the path toward becoming a second life-filled planet next door to our own. Patrick Barry of Science@NASA tells the story: "But that’s not how things turned out. Mars today is bitterly cold and bone-dry. The rivers and seas are long gone. Its atmosphere is thin and wispy, and if Martian microbes still exist, they’re probably eking out a meagre existence somewhere beneath the dusty Martian soil."

What happened? Why did Mars dry up and freeze over? These haunting questions have long puzzled scientists. A few years from now we might finally know the answer, thanks to a new orbiter NASA will send to Mars called MAVEN (Mars atmosphere and volatile evolution).

Planetary scientists believe that waterfalls may have once cascaded down these steep cliffs at Echus Chasma on Mars. Mars has many dessicated landscapes like this one, thought to have been sculpted by abundant water in the distant past. Credit: Mars Express/ESA.

According to Bruce Jakosky, principal investigator for MAVEN, University of Colorado, Boulder, the goal of MAVEN is to figure out what processes were responsible for those changes in the climate.

One way or another, scientists believe, Mars must have lost its most precious asset: its thick atmosphere of carbon dioxide. CO₂ in Mars’s atmosphere is a greenhouse gas, just as it is in our own atmosphere. A thick blanket of CO₂ and other greenhouse gases would have provided the warmer temperatures and greater atmospheric pressure required to keep liquid water from freezing solid or boiling away.

Over the last four-billion years, Mars somehow lost most of that blanket. Scientists have proposed various theories as to how that loss happened. Perhaps an asteroid impact blew most of the atmosphere into space in one catastrophic event. Or maybe erosion by the solar wind − a stream of charged particles emanating from the sun − could have slowly stripped the atmosphere away over eons. The planet’s surface might also have absorbed the CO₂ and locked it up in minerals such as carbonate. Ultimately, nobody knows for sure where all the missing CO₂ went.

MAVEN will be the first mission to Mars specifically designed to help scientists understand the ongoing escape of CO₂ and other gases into space. The probe will orbit Mars for at least one Earth-year. At the elliptical orbit’s low point, MAVEN will be 125 km above the surface; its high point will take it more than 6000 km out into space. This wide range of altitudes will enable MAVEN to sample Mars’s atmosphere more thoroughly than ever before.

As it orbits, MAVEN’s instruments will track ions and molecules in this broad cross-section of the Martian atmosphere, thoroughly documenting the flow of CO₂ and other molecules into space for the first time.

The loss of martian atmosphere could be caused by a complex set of mechanisms working simultaneously. MAVEN is equipped with eight different sensors designed to sort out the confusion.

Once Jakosky and his colleagues know how quickly Mars is losing CO₂ right now, they can extrapolate backwards in time to estimate the total amount lost to space during the last four billion years. "MAVEN will determine if loss to space was the most important player," Jakosky says.

But just as important as "how much?" is the question of "how?"

Conventional wisdom holds that Mars’s atmosphere is vulnerable because the planet lacks a global magnetic field. Earth’s magnetic field stretches far out into space and envelopes the whole planet in a protective bubble that deflects the solar wind. Mars has only regional, patchy magnetic fields that cover relatively small areas of the planet, mostly in the southern hemisphere. The rest of the atmosphere is fully exposed to the solar wind. So the loss could be caused by the slow erosion of the atmosphere in these exposed areas.

David Brain of UC Berkeley has proposed another, seemingly contrary possibility. These small magnetic fields might actually hasten the loss of Mars’s atmosphere.

The solar wind might buffet those magnetic field lines, occasionally pinching off a "bubble" of field lines that then drifts off into space − carrying a large chunk of the atmosphere with it. If so, having a partial magnetic field might be worse than having none at all.

Some evidence from NASA’s Mars global surveyor spacecraft supports Brain’s theory, but decisive measurements will have to wait for MAVEN, currently scheduled to launch in 2013.

For more details about the MAVEN mission visit http://lasp.colorado.edu/maven

SumbandilaSat payload activation going well

Activation of the various payloads on the SunSpace-designed and-built SumbandilaSat is progressing well, with some early successes recorded. Early on in the mission the camera was activated and some interesting video footage taken over Namibia was downloaded.

The ground control team reported on 3 November 2009 that they had completed a major attitude determination and control system (ADCS) software code upload to the satellite. As a result, the satellite is in a Nadir-pointing attitude and three axes stabilised. Nadir refers to the downward-facing viewing geometry of an orbiting satellite, such as when an astronaut faces the Earth while performing an EVA (spacewalk).

Hendrik Burger of SunSpace filling the butane tank, an important element to fuel the small engine that is used to control the orbit of the satellite.

The SA AMSAT-designed amateur radio experiment was successfully activated, first over South Africa and later over other parts of the world. Judging from reports received by SA AMSAT, SumbandilaSat has captured the interest of amateurs in Japan, Australia, New Zealand, Brazil, Europe, the USA and Canada.

The S-band data transmitter on the satellite was successfully activated and captured the transmitter-generated test pattern at the Overberg test range (OTB) station near Bredasdorp, Western Cape. During this exercise the satellite was in a target-tracking control mode, with the S-band waveguide antenna "tracking" the OTB station.

Test pattern.

The ground control team still has to activate and test several other experimental payloads before a regular operational schedule can be established and the control of the satellite can be handed over to the CSIR Satellite Applications Centre at Hartebeeshoek, Gauteng. For regular progress reports visit http://sumbandilamission.blogspot.com/

About astronomy stars

"I have yet to meet an astronomer who does not care about telling other people about the wonders of the universe. Astronomers share a passion for their science… and with that the battle for winning people’s hearts and minds is halfway won," says Marina Joubert, Media Stars coordinator, Southern Science, South Africa.

She collected tips and advice from astronomers around the world on how they communicate astronomy in a wide variety of ways to different audiences and assembled all the information on a website: www.saasta.ac.za/astronomystars

Nearly 50 astronomers from around the world contributed their ideas and experiences, often based on many years of involvement in communicating astronomy. As can be expected, their ideas differ and may even contradict one another… so it is up to the end-user to decide what may work best in a particular setting.

Giant ribbon discovered at the edge of the solar system

For years, researchers have known that the solar system is surrounded by a vast bubble of magnetism. Called the "heliosphere", it springs from the sun and extends far beyond the orbit of Pluto, providing a first line of defence against cosmic rays and interstellar clouds that try to enter our local space. Although the heliosphere is huge and literally fills the sky, it emits no light and no one has actually seen it − well, until now!

The galactic magnetic field shapes the heliosphere as it drapes over it. The ribbon appears to trace the area where the magnetic field is most parallel to the surface of the heliosphere (the heliopause). Credit: SwRI.

NASA’s IBEX (interstellar boundary explorer) spacecraft has made the first all-sky maps of the heliosphere and the results have taken researchers by surprise. The maps are bisected by a bright, winding ribbon of unknown origin.Scientists had no idea this ribbon existed, or what has created it. Previous ideas about the outer heliosphere will have to be revised.

Although the ribbon looks bright in the IBEX map, it does not glow in any conventional sense. The ribbon is not a source of light, but rather a source of particles − energetic neutral atoms or ENAs. IBEX’s sensors can detect these particles, which are produced in the outer heliosphere where the solar wind begins to slow down and mix with interstellar matter from outside the solar system.

IBEX is the latest in NASA’s series of low-cost, rapidly developed small explorers space missions. Southwest Research Institute in San Antonio, Texas led and developed the mission with a team of national and international partners. NASA’s Goddard Space Flight Center in Greenbelt, Maryland,

manages the explorers programme for NASA’s science mission directorate in Washington. Get more at: www.nasa.gov/mission_pages/ibex/index.html

Posted date: Monday, November 09, 2009 - 02:50 PM