The Sciences

The Next Decade of US Space Astronomy

Cosmic VarianceBy Julianne DalcantonAug 13, 2010 3:38 PM


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So, the Decadal Survey ("Astro2010") results are out. I missed the webcast (which I heard was of pretty sketchy quality), but read Roger Blandford's slides, and have skimmed or read a reasonable fraction of the preliminary report. Here's my summary and first reactions, broken down by regime. Steinn has also been blogging a running commentary of his reactions here. Space Missions: The top recommendation for a space mission is "WFIRST" -- basically a 1.5m wide-field IR imager in space, with low-resolution spectroscopy capabilities. This concept is the latest realization of what was previously known as "JDEM" (for "Joint Dark Energy Mission", which itself was an expanded and reconstructed version of "SNAP", the Supernova (SN) Acceleration Probe). The goal would be to use some combination of high redshift SNe, baryon acoustic oscillations (BAO), and weak lensing to constrain the parameters of dark energy. The committee recommended that the mission allow for a general observer (GO) program (thank goodness) and have a component dedicated to exoplanet discovery through microlensing (really? not really something I follow, but this isn't something I've heard much about. UPDATE: from the comments, Andy Gould has a white paper pointing out that the weak lensing requirements are essentially identical to what's needed for a microlensing-based planet search. Basically, you get it for free if you decide to pursue weak lensing. However, they did not take Andy's recommendation that the dark energy mission not pursue 3 independent techniques in one satellite.). The next recommendation is for a mixed portfolio of smaller satellite missions. These "Explorer"-class missions have historically been hugely successful -- WMAP, GALEX, etc -- but have been squeezed out recently by funding limitations and pressure from flagship mission development (JWST) and operations. The third recommendation is for continued development of LISA, an orbiting interferometric gravitational wave detector. LISA is a really nifty project -- one that I was not inately that interested in, but that became more and more compelling the more I learned about it. Co-blogger Daniel has thought a lot about LISA, and maybe we can get him to talk some more about it. Reactions to the Space Recommendations: Overall: These were hard choices, and reading the report, it's clear that a huge amount of weight was given to cost, feasibility, and competitiveness. IXO, the next generation flagship X-ray mission, dropped compared to its previous ranking, largely because the committee found it to be technologically and financially risky ("The Survey Committee also found IXO technologies to be too immature at present for accurate cost and risk assessment"). They instead flagged IXO as ripe for money for "technological development", so that it's ready to go for the next report. The Space Interferometry Mission (SIM, or SIMlite) dropped completely out, in large part due to cost vs scientific return. The real bummer about these recommendations is that entire subfields of US astronomy are pretty much shut out of the only environment where they can operate. X-ray, UV, and high-resolution astronomy (outside of IR and radio) are fundamentally space-based enterprises, and when Chandra and HST shut down, there will be nothing left, and nothing in the pipeline for a decade or more. The good times are continuing to role if you're an infrared astronomer -- (considering the series of Spitzer, WISE, JWST, and now WFIRST), but entire communities are going to be gutted. I do think that IXO will eventually get a start, because it's a strong mission, but are there going to be any X-ray astronomers left when it starts getting data? WFIRST: It will be interesting to see how this plays out, because two of the three dark energy techniques are going to making a fair bit of progress over the next decade, even without this mission -- two of the three new gigundo Hubble Multicycle Treasury programs will have a significant high-redshift SN component, and ground-based BAO surveys like BigBOSS are viable candidates for completion within a 10yr timescale. I'm sure discovery space will be left, but it will be interesting to see where we are in 10 years. There is also a highly ranked ESA mission with very similar capabilities. The only way it makes sense to go forward with WFIRST is if the projects somehow merge. Explorer Missions: There will definitely be broad community support for this recommendation. For certain wavelength regimes, this will be the only game in town. UV astronomers can probably make some real progress here, because there are huge gains that can be made by increases in detector efficiency, rather than by larger apertures, which are expensive to build and launch. High-resolution questions can't be addressed through the Explorer program, since you really need large baselines that are inaccessible at this cost limit (large baseline = big mirrors or interferometry = expensive). Not sure what can be done in the X-ray, but hard to go from Chandra or XMM down to what's available through this approach. LISA: I think LISA is pretty cool. I would have thought that the technological challenges for LISA are comparable to those that IXO faces, but I'll sensibly assume that the committee spent infinitely more time evaluating this issue than I have. Of the two, LISA probably has more pure discovery space potential. We at least know something about x-rays from space, but we know close to nothing about gravitational radiation from space. Ok, I gotta try to do some actually science today before I tackle the rest of the recommendations...more later

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