SKY_September2014.pdf

26 September 2014 sky & telescope

Winged Time Traveler

hundred million years — one doozy of a smash might have

excavated the giant depression in the planet’s northern

hemisphere. But it’s still unclear why the fi eld died and

whether it was a slow, peaceful death or a more violent one.

Either way, all that’s left is the remanent magnetism.

Trapped in the subsurface crust, these weak magnetic

bubbles rotate with the planet, making their interaction

with the magnetized solar wind incredibly complicated.

The solar wind can stretch them out like magnetic wind-

socks behind the planet. They partially shield Mars from

incoming energetic particles, although work by MAVEN

coinvestigator David Brain (University of Colorado at

Boulder) and others suggests that the solar wind might

occasionally snap off the tops of these windsocks, carry-

ing away pockets of atmosphere.

In fact, scientists aren’t even certain that a magnetic

fi eld is always a good thing for preserving a planet’s

atmosphere. The fi eld might instead help draw energy

from solar wind particles into the atmosphere, boosting

escape rates. Mars is a perfect place to test whether global

magnetism really acts as a “big sneeze guard,” as Brain

puts it, because the planet is only partially shielded.

Because MAVEN will dive down over diff erent parts

of the planet and at diff erent times of the Martian day,

its instruments will be able to study in detail how the

solar wind and the crustal fi elds interact. The spacecraft

is equipped to detect any crustal fi elds snapping off , but

whether it actually will detect these events depends on how

frequent the phenomenon is. Brain likens the process to a

dripping faucet: bursts of atmospheric escape probably hap-

pen intermittently, but there’s no steady stream.

Next Stop: Mars

MAVEN’s systems thus far check out A-OK. “I think the

hard work and incredible management — and I can say

that because that’s not me — is really showing itself now,

because everything is working exactly as expected,” says

Jakosky. He also notes (with perhaps a touch of glee) that

MAVEN has stayed on schedule and on budget.

It’ll take time to understand how the instruments are

working and to interpret the fi rst rush of data, so there

won’t be next-day results once the spacecraft enters orbit.

The team anticipates having preliminary results about

3 months after MAVEN arrives at Mars.

But perhaps by this time next year, we’ll have the

pieces we need to start solving the puzzle of how the most

Earth-like planet in our solar system (other than Earth

itself ) evolved from a clement world to the utterly desolate

one we see today. ✦

Mars’s crustal magnetic fi elds boggle assistant editor Camille

M. Carlisle’s mind. This article is based on her previous

coverage of MAVEN for S&T’s news blog and its special issue

Mars: Mysteries and Marvels of the Red Planet, published

earlier this year.

Watch videos from the MAVEN team about the

mission and the science behind it at skypub.com/

mavenvideos.

NASA’s MAVEN orbiter launched on November 18th without

incident, the beginning of a 10-month journey to the Red

Planet. Arrival is scheduled for late September 2014.

HAP GRIFFIN

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