We’re in an era of infrared astronomy… because we never left. Hot off the ‘presses’ (well, server, actually) is a paper in Publications of the Astronomical Society of the Pacific to continue the field.
The modern infrared age was marked by the launches of Spitzer (formerly IRTF, InfraRed Telescope Facility), Herschel (ESA’s far-IR telescope), and Akari (JAXA’s mission). But the IR age didn’t end after the several years that a space mission usually lasts. Spitzer continued in a warm mission, and was then complemented by WISE (which had its own warm mission). JWST then launched, and (knock wood) there were no problems. On the ground, larger and larger apertures at high, desert mountains allow infrared work on at least a partial basis. The coming ELT (Extremely Large Telescope) will, in a few more years, reach sensitivities previously limited to space missions only. And, by the time ELT is running, SPHEREx will fill in the gaps of both it and JWST. Because neither mega-project will have the time and survey power to reap the sky like a lawnmower.
Meanwhile, out of the limelight, other ground telescopes are doing IR work. On Maunakea, a site particularly good in IR, the UKIRT (United Kingdom InfraRed Telescope) and IRTF (NASA’s other InfraRed Telescope Facility) slog on. As we speak, the TAO (University of Tokyo Atacama Observatory) has been dedicated, and is having its final touches before regular observations.
I had already posted about IRTF. Now, in October’s issue of Pub. Astron. Soc. Pacific (vol. 136, issue 10, article 105003), we have a briefing paper on the refurbished MIRSI instrument for IRTF:
Hora, J. L. Trilling, D. E. López-Oquendo, A. J. et al. Design and Performance of the Upgraded Mid-Infrared Spectrometer and Imager (MIRSI) on the NASA Infrared Telescope Facility ad75ba
As I had posted, IRTF is the one telescope that handles the bulk of NASA’s Solar System follow-up characterization and monitoring. It’s true that Spitzer, Akari, Keck etc. can take infrared data on an asteroid/comet to determine size, type, composition, and other characteristics like surface roughness. But of all space and ground telescopes, IRTF just has that combination of capability and available schedule that made it the workhorse of this field.
A limitation of MIRSI was that to run at operating temperature it had to boil liquid helium. Hawaii is not a major industrial hub, and liquid helium led to a long, cumbersome, unreliable logistical train. The new MIRSI has a closed-loop cooler; not only does the helium last, but the flexibility is now enough for target-of-opportunity asteroids (i. e., short-notice, very-near-Earth objects). There is now an auxiliary, optical camera too. Part of characterizing asteroid size is comparing the expected infrared signature versus the optical brightness. An instrument with both channels makes this data point trivial to get and reliable to gauge. It’s not all good news, though. There is a loss of sensitivity versus its like-new performance (see Kassis et al. 2008)- “currently under investigation”.
The future looks bright- in multiple bands. SPHEREx will, by chance, catch asteroids that enter its field of view. Should such a body warrant further investigation- or just get missed by SPHEREx- it may be close and emissive enough for TAO, and maybe IRTF. Should something really warrant follow-up- say, a PHO (Potentially Hazardous Object)- then the big guns like JWST or ELT (perhaps GMT) would be diverted. This is “defense in depth”: any one of these characterization resources may be limited, but the pool of characterizers is broad and deep.