SKY_September2014.pdf

Winged Time Traveler

lest the drag forces act as aerobraking and alter its orbit.

The denser atmosphere might also facilitate sparking on

the instruments.

One thing MAVEN isn’t looking for is methane (CH 4 ),

despite multiple observations from Earth-based tele-

scopes and Martian orbiters suggesting that it exists in

the planet’s atmosphere. Methane is the most common

hydrocarbon in the solar system, but on Mars it’s unstable

on long time scales. Something must replenish it. On

Earth, that “something” is biological activity.

So far, NASA’s Curiosity rover has yet to sniff out any

methane, at least convincingly (S&T: Dec. 2013, p. 16).

MAVEN doesn’t have the spectroscopic range to detect

methane, but MOM does. The two teams hope to coordi-

nate some of their observations.

MAVEN will also complement Curiosity. While the

rover measures the composition of the well-mixed lower

atmosphere, the orbiter will watch the escape of spe-

cifi c gases high above. The rock samples that the rover

analyzes also contain embedded fi ngerprints from the

environment in which they formed. Those snapshots

of Martian history will help anchor the MAVEN team’s

extrapolations of atmospheric loss over time.

The team designed the mission to answer all its sci-

ence questions in one year, but the craft has enough fuel

to last about a decade. Mission planners purposefully

chose to have the orbiter reach Mars just after the solar

cycle reaches maximum, because solar activity is often

most volatile during this post-peak period. An extended

mission would provide more information about how the

changing solar cycle aff ects the planet’s atmosphere.

Magnetic Marvels

Mars doesn’t have a global magnetic fi eld today, but it

once did. Localized regions of magnetism, called rema-

nent fi elds, emanate from parts of the surface that both

melted (thanks to huge impacts, for example) and then

cooled back down during the early era when Mars still

had its global shield. As the rock cooled, the planet-wide

magnetic fi eld basically imprinted itself onto the crustal

material, remaining frozen in place long after the global

magnetosphere disappeared.

Mars’s global magnetic fi eld is long gone, but localized fi elds

(purple) still emanate from its crust. Some of these mini magne-

tospheres reach into the planet’s upper atmosphere.

The Indian Space Research Organ-

isation (ISRO) launched its own Mars

orbiter on November 5, 2013, two

weeks before NASA launched MAVEN.

India’s Mars Orbiter Mission, or MOM

— informally dubbed Mangalyaan

(“Mars Craft” in Hindi) — will study the

composition of the planet’s surface and

atmosphere from space.

Like MAVEN, MOM will arrive at

Mars in September. The Indian team

will maneuver the spacecraft during its

300-day interplanetary voyage with help

from NASA’s Jet Propulsion Laboratory,

using NASA’s Deep Space Network

to monitor the craft’s trajectory. After

MOM fi res a braking rocket, the space-

craft will slip into an elliptical orbit that

ranges from 350 to 80,000 km (220 to

50,000 miles) above the Martian surface

— signifi cantly farther out than MAVEN

will orbit.

The MOM spacecraft carries a sci-

ence payload of 15 kg (33 lbs) that

includes fi ve instruments: a Lyman-

alpha photometer, methane sensor,

quadrupole mass spectrometer, thermal

infrared imaging spectrometer, and tri-

color camera. These will work together

to conduct a global survey of the Mar-

tian atmosphere and surface.

One high-level objective is to look for

traces of methane. Although NASA’s

Curiosity rover has not conclusively

detected this gas from inside Gale Cra-

ter, Indian scientists point out that the

atmosphere in Gale might not refl ect

the situation across the Red Planet.

MOM might be the cheapest mission

to Mars ever fl own. In August 2012 the

Indian government approved $73 mil-

lion for this project — about one-tenth

of MAVEN’s $671 million budget. To

save money, the Indian space agency

used the ground systems and launch

vehicle already used for India’s lunar

orbiter, Chandrayaan-1, which operated

from October 2008 to August 2009.

Former S&T intern Shweta Krishnan is

a freelance journalist in Kilpauk, India.

India’s Mission to Mars

NASA / GSFC

24 September 2014 sky & telescope

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