Sky.and.Telescope_

instrument studies diff erent clues so that scientists can
put together the whole picture.
The instrument I work with is Alice, an ultraviolet
spectrometer led by principal investigator Alan Stern
(Southwest Research Institute). Alice is the fi rst UV
spectrometer to visit a comet and is one of three instru-
ments contributed by NASA to support this European-led
mission. With Alice, we’ll observe the comet’s surface and
the coma’s gas to fi gure out the relative proportion of cer-
tain elements and molecules. For instance, one of Alice’s
science objectives is to determine how abundant the noble
gases (e.g. helium, neon, argon) and molecular nitrogen
are in the gas coming from the nucleus. Both the trap-
ping of noble gases into cometary ice and their release are
temperature dependent, so based on the relative amounts
that we measure of those species and the timing of when
we detect them, we can deduce how cold it was in the cor-
ner of the solar system where the comet formed and the
history of C-G’s previous passes around the Sun.
We’ll also be able to tell how the temperature changes
inside the nucleus over time. Diff erent types of ices
sublimate at diff erent temperatures, so changes in the
proportions of the compounds coming out can reveal the
internal temperature.
Rosetta is an impressive spacecraft. The core is a
roughly 2.5-meter (8-foot) cube containing propulsion,
avionics, communications, computers, and all the instru-
ments. Star Trek fans might liken it to a small Borg space-
ship. What really stand out are the huge solar panels.
With a tip-to-tip wingspan of 32 meters and a collecting
area of 64 square meters, it’s the largest solar-power array
for any interplanetary spacecraft, just beating out the

Alice Ultraviolet Imaging Spectrometer

Analyzes gases in the coma and tail, measures UV surface properties

Comet Nucleus Sounding Experiment by Radiowave Transmission (CONSERT)

Uses radio waves to probe the comet’s interior

Cometary Secondary Ion Mass Analyzer (COSIMA)

Chemical analysis of dust grains, including composition and whether

they are organic or inorganic

Grain Impact Analyzer and Dust Accumulator (GIADA)

Measures the number, mass, momentum, and velocity distribution of dust

grains coming from the nucleus and from other directions (refl ected by solar

radiation pressure)

Micro-Imaging Dust Analysis System (MIDAS)

Provides information on population, size, volume, and shape of dust grains

Microwave Instrument for the Rosetta Orbiter (MIRO)

Determines abundances of major gases, surface outgassing rate, and the

nucleus’s subsurface temperature

Optical, Spectroscopic, and Infrared Remote Imaging System (OSIRIS)

Wide-angle and narrow-angle cameras

Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA)

Chemical analysis of the comet’s atmosphere (composition, particle velocities,

and reactions)

Rosetta Plasma Consortium (RPC)

Five sensors; examine the nucleus’s physical properties and the inner coma’s

structure, monitor activity, study comet’s interaction with the solar wind

Radio Science Investigation (RSI)

Measures the nucleus’s mass and density, defi nes comet’s orbit, and studies

the inner coma

Visible and Infrared Thermal Imaging Spectrometer (VIRTIS)

Maps nature of the solids and temperatures on the nucleus’s surface, identi-

fi es comet gases, and characterizes the coma’s physical conditions

Rosetta’s OSIRIS Narrow-Angle Camera took this image of
Comet C-G (circled) on April 30th from more than 2 million
kilometers away. The 12-minute exposure reveals the growing
dusty coma. The globular cluster M107 shines at left.

ESA / ATG MEDIALAB

ESA / ROSETTA / MPS FOR OSIRIS-TEAM MPS / UPD / LAM / IAA / SSO / INTA / UPM / DASP / IDA

COSIMA

ROSINA DFMS

GIADA

ROSINA COPS

CONSERT

VIRTIS

OSIRIS NAC

Philae

OSIRIS WAC

MIDAS

MIRO

RPC IES

ROSINA RTOF

RPC ICA

RPC MIP

RPC LAP

Alice

RSI (uses antenna)

RPC MAG

RPC LAP

Instruments on Rosetta Orbiter