NASA's Twin Mars Probes Swing Past Earth for a 9-Minute Speed Boost

NASA's two ESCAPADE spacecraft are set to fire their thrusters close to Earth on Nov. 7 and Nov. 9, using the planet's gravity as a slingshot toward Mars, according to Universe Today. Once there, the pair are expected to be the first spacecraft to fly in formation around Mars as they study how the planet lost its ancient atmosphere.

Some skywatchers may be able to spot them as they pass, though Universe Today says a telescope will almost certainly be needed.

What will the spacecraft do near Earth?

The twins, named Red and Blue, will pass Earth at a distance of about 965 to 1,770 kilometers above the surface. There they will fire their thrusters and combine that push with Earth's gravity to swing onto a path to Mars. Universe Today reports that the first spacecraft will do this on Nov. 7 and the second on Nov. 9.

Each burn, called a trans-Mars injection burn, is expected to last about 9 minutes. It should raise each spacecraft's speed from about 10.14 km/s to 10.78 km/s, a gain of more than 2,000 km/hour.

Why do they need this maneuver?

ESCAPADE did not launch during the usual Mars launch window, which comes around every 26 months, Universe Today reports. Instead, the spacecraft waited for a time near the Earth-Sun Lagrange point 2, then returned toward Earth to use the burns to power their way to Mars.

The detour produced some extra science. According to the report, the spacecraft flew through Earth's magnetotail, the stretch of Earth's magnetic environment trailing away from the Sun. They were the first spacecraft to do so, and the observations are expected to be shared soon.

What are they trying to learn at Mars?

Evidence is growing, though not yet conclusive, that Mars was once warm and wet and may have been habitable. That would have required a much thicker atmosphere than the thin, carbon dioxide-dominated one it has today. Scientists generally propose that ultraviolet radiation from the Sun drove the old atmosphere into space after Mars lost its protective global magnetic field.

Mars still has patches of magnetism in its crust, left over from when its core generated a global field. These patches also create local magnetic fields in the upper atmosphere. ESCAPADE, short for Escape and Plasma Acceleration and Dynamics Explorers, will measure how the solar wind interacts with these remnants. Universe Today notes that the broad picture of atmosphere loss is clear but the finer details are not.

Why send two spacecraft instead of one?

Interactions between the solar wind and magnetic fields can change within very short periods. A single spacecraft cannot tell whether a change in its readings reflects a change in those interactions or simply its own movement. Two spacecraft flying together can separate the two effects.

In the first part of the mission, Science Phase A, which lasts about 6 months, the pair will share an orbit at varying distances from each other, in a formation NASA calls the “String of Pearls.” In Science Phase B, they will work more independently. Blue will lower its orbit to about 7,000 km, and Red will raise its orbit to about 10,000 km. That phase lasts about 5 months and ends the nominal science mission. According to Universe Today, the spacecraft should keep operating for many years afterward, and NASA will have decisions to make then.

Why does it matter?

For most readers, the practical takeaway is scientific rather than financial or political. Mars offers a nearby example of a planet that may once have been habitable and then lost that quality. Universe Today's author argues that studying how this happened could inform the search for life elsewhere and put Earth's long-lasting habitability in perspective. That is the author's framing, not a finding of the mission.

For backyard observers, the spacecraft are described as a pair of dim, refrigerator-sized objects moving against the stars. Seeing them would require a telescope and likely some luck.

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Around Prague, based on reporting by Universe Today