[meteorite-list] Could Upcoming Comet Flybys Damage Mars Spacecraft?

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu, 19 Sep 2013 12:07:29 -0700 (PDT)
Message-ID: <201309191907.r8JJ7TfD000584_at_zagami.jpl.nasa.gov>

http://www.space.com/22859-mars-spacecraft-comet-flybys-dangers.html

Could Upcoming Comet Flybys Damage Mars Spacecraft?
By Leonard David
space.com
September 19, 2013

Two comets will buzz Mars over the course of the next year, prompting
excitement as well as some concern that cometary particles could hit the
spacecraft orbiting the Red Planet and exploring its surface.

Three operational spacecraft currently circle Mars: NASA's Odyssey and
Mars Reconnaissance Orbiter (MRO), as well as Europe's Mars Express. NASA
also has two functioning rovers, Curiosity and Opportunity, on the ground
on Mars.

All of these spacecraft will have ringside seats as Comet ISON cruises
by Mars this year, followed by Comet 2013 A1 (Siding Spring) in 2014.

Crossing the sublime line

The MRO spacecraft has been on the lookout for Comet ISON, said Richard
Zurek, MRO project scientist and chief scientist in the Mars Program Office
at NASA's Jet Propulsion Laboratory (JPL) in Pasadena, Calif.

On Aug. 20, MRO looked for Comet ISON, which experts say could put on
a dazzling sky show here on Earth shortly after the icy wanderer zips
a scant 724,000 miles (1.16 million kilometers) above the surface of the
sun on Nov. 28.

During last month's observation by MRO, ISON was 1 astronomical unit (AU)
from Mars and 2.5 AU from the sun. (One AU is the distance from Earth
to the sun - about 93 million miles, or 1.5 million km.)

Given ISON's distance from the sun, the comet should have crossed the
solar system's "snow line" by that time, Zurek told SPACE.com. At the
snow line, many comets brighten as ice more rapidly sublimes into gas
due to increasing solar radiation.

"The MRO instruments did not see anything," Zurek said, and evidence suggests
the instruments "were pointed accurately. Thus, the current conclusion
is that the comet had not brightened quite enough to be seen at that range
with the MRO instruments."

Comet ISON's current luminosity is a topic of much discussion among astronomers
and skywatchers alike. The icy wanderer was branded a "comet of the century"
candidate almost immediately after its discovery in September 2012, but
recent observations suggest that it's not brightening as much as expected
or hoped on its trek toward the sun.

More observations ahead

MRO will look at ISON again, Zurek said, with observations scheduled for
Sept. 29, Oct. 1 and Oct. 2 (when the comet will be closest to Mars).
At those times, ISON will be roughly 14 times closer and will likely be
relatively easy to detect.

"At the closest passage distance, there is no concern that cometary particles
from ISON will affect the orbiters or Mars," he said.

NASA's 1-ton Curiosity rover and its smaller, older cousin, Opportunity,
will also image ISON from the Martian surface later this month, Zurek
said. However, those plans are still being formulated.

The spacecraft in orbit around Mars and on the planet will give scientists
a better chance of investigating Comet ISON, though that is not their
primary function, said Michael Meyer, lead scientist for NASA's Mars Exploration
Program at the agency's headquarters in Washington, D.C.

"Mars has a better view than Earth does right now," Meyer said. However,
it is "challenging for orbital and landed assets as they are not really
designed to do this sort of thing. They are supposed to be looking at
Mars."

Meyer spoke via Skype Aug. 25 during a New Media Practitioners Professional
Development Workshop on the upcoming launch of NASA's Mars Atmosphere
and Volatile Evolution orbiter (or Maven for short). The workshop took
place at the University of Colorado Boulder's Laboratory for Atmospheric
and Space Physics (LASP).

Another comet coming

After ISON, scientists will look forward to Comet Siding Spring, Meyer
said. That comet will make a very close approach to Mars in October 2014,
skirting just 76,428 miles (123,000 km) from the planet, according to
the current best estimates.

"That promises to be pretty exciting," Meyer said. "Right now, in all
honesty, what we know about it and what sort of calculations can be done
- the error bars are extremely large."

The comet poses risks to orbiters circling Mars, Meyer said, a prospect
that may lead to re-orienting and maneuvering of the craft to protect
them from comet particle strikes. But whether it's a 10 percent, 1 percent
or 0.1 percent risk remains unknown at the moment, he said.

"You can't get too worked up about it until you get some measurements
as the comet gets closer," Meyer said. "It promises to be quite a show
- if we're able to look at it."

Stay tuned

In early August, JPL issued a request for proposals to help characterize
the cometary environment of Comet Siding Spring, with proposals due on
Sept. 11.

"The intent is to provide data products useful for risk assessment and
mitigation-strategy development for the Mars orbiter missions, due to
possible impacts from dust and ion tail particles as this comet encounters
Mars," the JPL request stated.

Model simulations are needed to characterize the evolving dust and ion
particle distributions around Comet Siding Spring, as well as their motions
with respect to Mars, as this comet approaches the Red Planet.

Because Comet Siding Spring will come so close to Mars, it's likely that
the planet, along with its associated spacecraft, will pass through the
coma of the comet, Zurek said. But NASA's rovers will probably be relatively
well protected, he said.

"As thin as the Mars atmosphere is, it should still shield the rovers
from infalling particles," Zurek said, "so the risks to be assessed are
to the orbiters."

Zurek told SPACE.com that scientists won't have an idea of how big a risk
the comet environment will pose until they make more observations of the
comet's variability as it nears the sun.

"We have put out a call for modeling of the cometary environment," Zurek
said. Such modeling, he said, is dependent on the developing comet activity.

Passage through the comet's coma could result in a wide range of effects:
anything from a modest enhancement to the background meteoritic flux experienced
by the spacecraft, which is deemed most likely, to something more substantial,
Zurek said.

"So stay tuned!" he said.

New arrival

Siding Spring's Mars visitation will also overlap with that of another
Mars newcomer, NASA's Maven spacecraft. To be launched this November,
it will arrive at the Red Planet in late September 2014, with Comet Siding
Spring set to make its closest approach to Mars on Oct. 19.

However, that will likely be too soon for the Maven orbiter to analyze
the comet.

"Maven will still be in the middle of its commissioning phase at that
time and will not be ready to take regular measurements," said Bruce Jakosky,
principal investigator for Maven at LASP.

"Although we'd like to be able to observe the comet as it passes by and
how it affects the upper atmosphere, our first priority will be spacecraft
and instrument health and safety," Jakosky told SPACE.com.

The Maven team is working with the Mars Program Office (MPO) to predict
the likely dust environment as the comet passes by, and how impacts from
the dust might affect the spacecraft, Jakosky said. The MPO is coordinating
the activities, he said, as that group is concerned about Mars Odyssey
and MRO, in addition to Maven.

Minimizing the risk

"After Maven's launch, we'll be looking in detail at what mitigations
we can take to minimize any risk," Jakosky said. "We'll look at things
such as turning the least-vulnerable face into the flow of the dust, putting
the solar panels edge-on to the flow and so on."

Jakosky said that, at this point, the best analysis indicates a minimal
risk to Maven.

The number of dust impacts expected, and the effect they'll have on the
spacecraft should be within the range of what Maven researchers anticipated
for a normal mission run, Jakosky said. That is, the dust impacts should
not exceed what researchers had already planned to absorb just from interplanetary
dust over the lifetime of the mission, he said.

"I do expect that telescopic observations of the comet in the spring and
more-detailed modeling of the dust environment in the coma and tail will
help us to refine our analysis," Jakosky said.
Received on Thu 19 Sep 2013 03:07:29 PM PDT