- 3853
- TELESCOPES - work
together? Is it possible for Earth
and space-based telescopes to work together? Astronomers wrote a white paper
that points out the potential benefits of coordinating ground, orbital and in
situ based observations of objects.
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---------------------- 3853
- TELESCOPES - work
together
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- The full electromagnetic spectrum with the
different sub-bands labeled.
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-
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- The electromagnetic spectrum is extremely
large. It includes all types of light,
such as radio, infrared, x-rays, ultraviolet and visible light. There is no one single sensor that can
collect data in all of those different wavelengths at the same time. Therefore, scientists have developed a
plethora of instruments that are extremely good at collecting data in one
specific spectrum, such as radio (ALMA), or mid-range infrared (James Webb).
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- The down side of this specialization is
that those instruments are blind in other spectral ranges. If a scientific team is only observing in one
type of light, there is a chance that they could miss important aspects of a
phenomena they are studying that are only visible in a different spectral band.
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- Much of the planetary science data
collected is the result of spacecraft that are sent to a planetary system to
perform in situ observations. However,
due to the high cost of developing space-based systems and then launching them
into orbit, mission planners for these in situ missions must be very selective
about what types of instruments they allow on board their spacecraft. What this normally means is that they are not
able to bring imagers that are capable of covering the entire electromagnetic
spectrum.
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- That is where coordination with ground and near-earth-orbit
based telescopes comes in. There are
many telescopes in those locations, such as the Atacama desert or Hawaii’s
Mauna Kea, that are extremely large, and can provide very high resolution
images in specific spectral bands, such as radio, microwaves, or infrared.
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- Infrared is particularly useful as there is
a lot of physical data points that can be obtained in a single measurement,
such as pressure, temperature, and molecular abundances. If we can coordinate
observations with these much larger, specialized observatories, they will no
longer need to include them on their own spacecraft. However, if they are unable to coordinate
simultaneous observations, then they would lose out on the spectra that the
observatories closer to home can provide.
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- Another advantage that earth-based
observatories have over their in situ counterparts is their ability to image a
whole planet at once. Many orbiter or
fly by missions are only capable of measuring part of their subject at a single
point in time.
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- This results in a loss of contextual
understanding, as dynamic phenomena that might be observed in a single place by
the in situ spacecraft might not be present over the entire surface of the
planet or moon. Support from earth-based
telescopes, whether on the ground or in space, could provide that larger
context that the spacecraft itself lacks.
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- This sort of coordination to cover all of
the spectral bases has already been accomplished with one in situ planetary
mission: the Juno spacecraft currently in orbit around Jupiter. The resulting coordination between the Juno
spacecraft and a series of earth-based observatories resulted in over 40 papers
that used data from more than one observational source of the Jupiter system
during that time.
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- Three separate images captured as part of
the Juno multi-spectral survey shows the same segment of Jupiter simultaneously
in three different wavelengths.
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- The orbiters around Mars provide excellent
two-dimensional slices of spectral data as they are passing over a specific
strip of the planet. However,
observatories closer to Earth can provide data on the entire hemisphere of the
planet that is facing them, and add a layer of depth that would allow
scientists to piece together a three-dimensional picture that would be
impossible using only data from the orbiters.
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- There are still some limitations to
earth-based observations, such as the fact that methane is present in Earth’s
atmosphere as well, which could skew the data when looking at Mars.
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- To get around this problem, scientists came
up with an ingenious method of only observing Mars while it is moving away from
(or toward) Earth at more than 13km a second.
This differential speed red- (or blue-) shifts the spectral signature of
the Martian methane enough that it can be differentiated from that simply
present in Earth’s atmosphere.
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- Another particularly interesting target of
joint observations is Titan, which has been the subject of intense scrutiny in
recent years due to its hydrocarbon lakes, and its methane/ethane based
hydrological cycle.
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- The moon is so interesting it is about to
receive it’s own in situ visitor in the form of the Dragonfly mission. When Dragonfly lands in 2034, the white paper
team hopes that many Earth-based telescopes will turn their eyes toward Titan,
as the data collected from the surface can then be coordinated with more remote
observations.
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- Dragonfly will be equipped a mass
spectrometer, which allows the detection of molecules which are impossible to
see remotely, and reveals the full composition of the atmosphere. Earth-based observation could in turn provide
context for these measurements.
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- Dragonfly's lander will be the first to
reach Titan's surface, and can provide local data to any coordinated
observation program. Those combined
observations will focus on the organic chemistry that is taking place on the
moon. A particularly useful Earth-based
tool is ALMA, the observatory that held the conference that kicked off the
white paper. ALMA is a series of radio
telescopes, which are particularly good at observing organic compounds and
making detailed maps of its observational subjects. Both capabilities would be particularly
helpful in helping the Dragonfly mission, and ALMA’s operators are already very
familiar with Titan.
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- The array actually used Titan as a
calibration target for a number of years after it first launched, due to its
brightness and seeming stability. The
wealth of observations allowed researchers to study Titan and the evolution of
its atmosphere, revealing dynamic processes, and leading to improved
understanding of the moon.
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- Unfortunately, it also revealed Titan is
actively changing, making it less suitable as a flux calibration target. The ALMA team then switched to using a pulsar
for future calibrations.
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January 28,
2022 TELESCOPES - work
together? 3853
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--- Monday, January 30,
2023 ---------------------------
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