- 3949 - ASTRONOMY - using multiple combined sources? How do imaging systems interact with different wavelengths of light? 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.
------------ 3949 - ASTRONOMY - using multiple combined sources?
- 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).
-
- 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.
-
- 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.
-
- 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.
-
- 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 a mission
planner of a planetary exploration spacecraft mission 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.
-
- Many
orbiter or fly by missions are only capable of measuring part of their subject
at a single point in time. 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. 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.
-
- Mars is of
particular interest, as it is the most studied planet outside of Earth, and the
only one with active rovers physically on its surface. Scientists interested in understanding where
the methane from Mars’ atmosphere comes from would certainly benefit from a
coordinated observational campaign between several of the orbiters around Mars.
-
- 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.
-
- 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. 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.
-
- 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.
-
- 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.
-
- 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.
-
- Dragonfly's
lander will be the first to reach Titan's surface, and can provide local data
to any coordinated observation program. The mission will prove an excellent
opportunity for coordinated observations. It can provide on the ground data
that can be contextualized with other, larger observatories.
-
- Those
combined observations will focus on the organic chemistry that is taking place
on the moon. 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.
-
- 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.
-
-
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.
-
- Waves that
are created as solar winds pummel Earth's magnetic field appear to escape the
turbulent region around our planet, but how they do so has remained a
mystery. How these waves seem to
survive?
-
- They
continue past the leading "foreshock" region to an area called the
"shock" and then create "clone" waves with identical
qualities. So, what astronomers had
been observing for decades was not the waves created by the solar winds but
rather the waves' newly produced "clones."
-
- The
magnetosphere is a magnetic bubble that protects Earth from charged particles
from the sun called the solar wind by funneling these particles down
magnetic-field lines and to the other side of our planet. The interaction
between the supersonic solar wind and the terrestrial magnetic field creates
the shock region, also known as the bow shock. The foreshock then forms
"upstream" of this shock region.
-
- The impact
of solar winds causes electromagnetic waves to appear as small oscillations of
Earth's magnetic field. Waves with the same oscillations as waves in this
foreshock region have been spotted on Earth's sun-facing side, suggesting that
they can enter the magnetosphere and travel all the way to the planet's
surface.
-
- But how
could these waves cross the violent shock region and remain unchanged? Astronomers found waves on the other side of
the shock region that had properties that were almost exactly the same as those
in the preceding foreshock area.
-
- At first,
astronomers thought that the initial theory proposed in the 1970s was correct:
the waves could cross the shock unchanged.
But, there was an inconsistency in the wave properties that this theory
could not reconcile, so we investigated further. Eventually, it became clear
that things were much more complicated than they seemed.
-
- The waves we
saw behind the shock were not the same as those in the foreshock, but new waves
created at the shock by the periodic impact of foreshock waves. The team thinks that when solar winds flow
across the shock, they compress and heat it, with the strength of the shock
determining the extent to which this happens.
-
- The peaks
and troughs in waves coming from the foreshock "tune" the shock as
they arrive at it and make it alternate between periodically weak and strong
space weather.
-
- This then
creates new waves from the shock that are thus in concert with the foreshock
waves.
-
April 7, 2023 ASTRONOMY -
using multiple combined sources? 3949
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