Monday, April 10, 2023

3949 - ASTRONOMY - using multiple combined sources?

 

-    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).

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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.

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-   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.

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-    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.

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-     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.

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-    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.

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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.  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. 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.

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-    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.

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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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-     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?

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-   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."

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-     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.

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-    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.

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-   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.

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-  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.

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-   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.

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-   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.

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-   This then creates new waves from the shock that are thus in concert with the foreshock waves.

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                   April 7, 2023         ASTRONOMY  -  using multiple combined sources?         3949                                                                                                                          

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