Friday, February 17, 2017

THEMIS - Θέμις

Μια δεκαετία ζωής της διαστημικής αποστολής THEMIS (Time History of Events and Macroscale Interactions during Substorms) - έμπνευσης και τέκνου του αγαπητού φίλου και συμφοιτητή Βασίλη Αγγελόπουλου, καθηγητή του UCLA. Η Θέμις (προφανής η παραπομπή στη θεά της δικαιοσύνης) γέννησε με τη σειρά της την Άρτεμη (ARTEMIS - Acceleration, Reconnection, Turbulence and Electrodynamics of the Moon’s Interaction with the Sun), όταν οι δύο από τους πέντε δορυφόρους απομακρύνθηκαν από τη Γη και μπήκαν σε τροχιά γύρω από τη Σελήνη. Ακολουθεί μια ανακεφαλαίωση των επιτυχιών της αποστολής από τον ίδιο τον Βασίλη:

Who would have imagined 10 years ago to the day, when that Delta-II 7920 rocket took our five spacecraft to their coast (1.1x15Re) orbit, that THEMIS and ARTEMIS would be still trailblazing new research directions, and would be the centerpiece of the Heliophysics System Observatory? With hardware as good as new (in fact the FGM is getting better with time!) we can honestly be planning to utilize the several kg of fuel still on-board to address yet new science objectives for years to come.

It has been a journey of tremendous science breakthroughs. The location of substorm onset, the link of magnetic reconnection and the inner magnetosphere, the propagation of flux bundles leading to particle injections and elemental wedgelets, the generation of north-south arcs and their collisions with pre-onset arc resulting in explosive substorm onsets - signifying the triggering of energy dissipation at the inner magnetosphere, the location of the pre-existing aurora, and countless other discoveries have revealed the nature of magnetotail dynamics and ionospheric coupling. On the dayside, discoveries on the complex nature of magnetopause and foreshock disturbances, with global ramifications has also emerged. At lunar distances new aspects of the solar wind interactions with the lunar exosphere, surface and crustal anomalies were explored, while upstream and tail phenomena such as the foremoon region, and mid-tail asymmetric reconnection have been discovered. The ground based observatories have enabled novel views of our global magnetosphere and have been part-and-parcel of many of our mission highlights.

Today the spacecraft are being operated in unique ways, and are destined for further discoveries. Low energy captures on ESAs on THEMIS-A enable a finer view of the cold ion and electron populations, while Ultra-Fast Surveys (6min captures of continuous waveforms – easily recognized by the ciel-shaded pieces of the modes bar in overview plots) enable an unbiased look at the wealth and relative importance of plasma waves in the near-Earth magnetosphere. At the same time, the orbits are being controlled to stay in conjunction with MMS from opposite sides of the magnetosphere, and our collaborations with MMS, Van Allen Probes, ERG(Arase) and many other Heliophysics Observatory missions are expanding though a powerful set of analysis tools in SPEDAS.

The missions’ future is equally promising as it was at launch, now poised to answer some of the most cutting-edge questions in the field. Aside from tuning the orbits to make for a powerful HSO and engaging the community in doing so, our new orbits will have apogees as high as 15Re, exploring comprehensively, for the first time, the inner edge of the plasma sheet’s interaction with the reconnection outflows and the magnetopause near the terminator. We will be asking: What is the process by which most magnetic energy is converted to heat driving the ring current and ionospheric currents? What is the role of foreshock transients in acceleration of some of the most energetic particles in the upstream region? How do dayside localized transient activations lead to flux transport over the poles and geoeffective reconnection in the mid-tail (ARTEMIS)? Is magnetic reconnection in the tail driven or spontaneous and what determines its location and rate? These are some of the most vexing questions in our field right now, with implications for other planetary and astrophysical settings. We will be discussing the extended mission plans (outlook beyond 5 years, just as exciting) at our next SWT opportunity.

Here’s to our mission operations team that keeps our spacecraft safe and well-functioning! Here’s to our creative science team that maintains the spirit of discovery strong, doing justice to the novelty of the incoming data! And here’s to NASA that recognizes innovation and its implications for the future of Heliophysics, and enables our contributions. 

No comments:

Post a Comment