Space Topics: MESSENGER
Mission Objectives
MESSENGER is designed to answer six main questions about Mercury, most of
which were inspired by Mariner 10's surprising flybys of Mercury in 1974 and
1975.
1. Why is Mercury so dense?
Although it is not the densest planet in the solar system -- that distinction
belongs to the Earth! -- Mercury's high density implies that it is about
two-thirds iron metal (Earth has only half that much). This question is
important to our understanding of how our solar system formed.
Discovery Rupes, Mercury
Discovery Rupes is a scarp that cuts across several impact craters.
Geologists interpret it to be a feature that formed when Mercury
shrank as it cooled. Mercury's crust fractured and buckled, forming
the scarp. This Mariner 10 image covers an area about 55 kilometers
across. Credit: NASA/JPL/Mark Robinson |
2. What is Mercury’s geologic history?
Mercury has an ancient geologic surface, but it also has a magnetic field.
How can the surface be frozen in time while the planet has an active core?
Geologists will try to answer this question by mapping the whole surface
of the planet, capturing images, recording the surface chemical composition,
and measuring the shape of landforms to determine the geologic history.
This includes photographing the 55% of the planet that has never been observed
by a spacecraft.
3. What are the structure and state of Mercury's core?
Mercury's core is huge for the planet's size. Mercury is small enough that
the core should be solid; but it has a magnetic field, implying that the
core is liquid; but the surface is geologically old, so there shouldn't
be a liquid core. No one really knows how such a large core behaves. MESSENGER
will probe the core by studying its effect on Mercury's gravity field.
4. What is the nature of Mercury's magnetic field?
Is it really like Earth's magnetic field in miniature? Or does it arise
from a completely different process? And how does it interact with the Sun's?
5. What are the unusual materials at Mercury's poles?
Earth-based radar observations of Mercury hint at different surface materials
lurking in the floors of polar craters that have been in permanent shadow
for billions of years. Could it be water ice?
6. What volatiles are important at Mercury?
The gases forming Mercury's "air" are so incredibly thin that scientists
don't call it an "atmosphere," they call it an "exosphere." Six
elements are known to exist in Mercury's exosphere: (1) hydrogen, (2) helium,
(3) oxygen, (4) sodium, (5) potassium, and (6) calcium. How abundant these
are, and how they got into the exosphere, will answer questions about what
processes have shaped the surface of Mercury since it became geologically
inactive.
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