LSST's Contribution to NEO Detection and NASA Collaboration
LSST's potential contribution to near-Earth object detection, mission extension considerations, ongoing discussions with NASA, concerns in the Solar System community, Mario's task force, and challenges in convincing the community.
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Interactions with the External Community: NEOs and Euclid/WFIRST Steven M. Kahn LSST Director SAC Meeting, November 16, 2015 Science Advisory Committee Tucson November 16, 2015 Science Advisory Committee Tucson November 16, 2015 1
LSST and Near Earth Asteroids We have argued all along that LSST has the capability to make a major contribution to NEO detection, and can possibly meet the Congressional mandate (90% efficiency down to 140 m) if we extend the mission to 12 years, and optimize the observing strategy. This has raised the possibility of having NASA contribute to LSST Operations a major advantage if we can get it. We had one official meeting with NASA officials in Washington, and there has been on-going discussion between NASA and NSF, but we have no formal agreement so far. Some in the NEO community have publicly questioned our claims about LSST s capabilities in this area, undermining our credibility. I have asked Mario to lead a task force addressing this concern. Science Advisory Committee Tucson November 16, 2015 2
LSST and Near Earth Asteroids LSST's plan right now is to detect asteroids by 1) Obtaining a pair of observations of a given field during the same night, and then re-observing enough sky to guarantee that a large fraction of asteroids will be detected in three different nights during a 2-week long window. 2) The pairs of detections in a given night, called tracklets, will be combined into tracks using simple trajectories (e.g. parabola); these tracks will also include false associations of tracklets, as well as false tracklets due to processing artifacts. 3) Keplerian orbits will be fit to the tracks, which will both yield orbital parameters for real objects and reject false positives (due to false tracklets, or false associations of tracklets into tracks). Science Advisory Committee Tucson November 16, 2015 3
LSST and Near Earth Asteroids The Solar System community is concerned about how effectively this can be done. There are a number of reasons, but the most often cited one is the failure of Pan-STARRS to execute a similar scheme due to an exceptionally high rate of false positives in their difference images. Another question concerns the ability of MOPS (the Moving Object Processing System) to do the linkages with many false-positive tracklets . A third concern is about our assumption that interesting NEOs and PHAs stick around for long enough to be detected with our scheme. LSST team has plausible arguments as to why LSST is different, but it's difficult to convince the community with just those. On the other hand, it's also difficult to do an actual demonstration w/o the real software in hand; and we won't have that until ~2018. Science Advisory Committee Tucson November 16, 2015 4
LSST and Near Earth Asteroids Mario s worked on a study that addressed three sets of issues: What are the detection and false-positive rates that we can expect from LSST-like difference images, based on running the LSST image differencing pipeline prototype on LSST-like data (DECam and HSC)? Assuming those detection and false-positives rates, and assuming the current LSST baseline cadence, with what efficiency can LSST's MOPS link the detections into orbits (i.e., if we detect an object on an image twice per night, in three nights, over two weeks, what is the success rate of MOPS in linking the three pairs into an orbit). Given the linking success rate above, and a synthetic population of NEOs (e.g., Bottke's or Greenstreet et al. 2012 model), how many of them will the LSST detect, as a function of absolute magnitude (or size). Science Advisory Committee Tucson November 16, 2015 5
LSST and Near Earth Asteroids A paper is now out on the arXiv. It shows that the current candidate baseline cadence achieves ~70% discovery rates for NEOs, and is robust to various perturbations (i.e., things that may go wrong don t immediately doom the project the detection rate doesn t drop to zero). Preliminary work on #1, getting the LSST image differencing routines to work on DECam data is already done; more will be done in the next ~month and a half. The same is true of #2. Sometime by this year s end, we hope to have a longer paper describing the results of the study, that will hopefully be reassuring to the solar system community, as well as give the necessary, actionable, information to all the agencies involved. Science Advisory Committee Tucson November 16, 2015 6
Interactions with External Community A similar study of LSST performance has been launched by the JPL group led by Steve Chesley. The LSST group is closely collaborating with the JPL group on tool development and characterization of LSST cadence, image differencing and MOPS performance. The JPL report, based on LSST characterization provided by the LSST group, will be submitted to NASA, and used in the evaluation of whether or not NASA should contribute to LSST ops. LSST will produce NEO-optimized cadence simulations during early 2016 which will test the limits of what is possible with LSST in the NEO context (e.g. can 70% completeness expected for baseline cadence be boosted to 90%?), and will also assess the impact on such optimization on other science programs. Science Advisory Committee Tucson November 16, 2015 7
Joint Pixel Level Processing with Euclid and WFIRST Euclid is a European Space Agency mission designed to address dark energy by conducting a space-based visible and IR imaging survey + an IR spectroscopic survey. WFIRST is a planned NASA mission designed to conduct a high spatial resolution IR imaging survey + a spectroscopic survey. In both cases, they require ground-based visible-band imaging to determine photometric redshifts for their detected galaxies. LSST is clearly the optimal facility to supply these visible band colors in the South. There are significant systematic effects that will be encountered if we simply combine catalogued fluxes determined separately by each of the missions. The way to avoid this problem is to re-reduce all of the pixel-level data jointly, using the same apertures, centroids, etc. There are other benefits to joint pixel-level processing, eg using the higher resolution space- based images to deblend the LSST images, using the IR colors of stars together with LSST data for astronomical investigations, etc. Science Advisory Committee Tucson November 16, 2015 8
Joint Pixel Level Processing with Euclid and WFIRST A joint analysis of LSST data together with Euclid and WFIRST data is outside the scope of the current LSST Project. This applies to both figuring out how to do it, and implementing it in operations. It is also outside the scope of the NASA-supported US effort on Euclid, and the anticipated NASA-supported data processing effort for WFIRST. Therefore, we could not entertain serious discussions of this until we got a blessing from the agencies that they were interested in this. That occurred in December, 2014. At that time, all three expressed interest in convening a meeting on this topic. We held that meeting in June, one rep from each project, plus the appropriate people from NSF, DOE, and NASA. Science Advisory Committee Tucson November 16, 2015 9
Joint Pixel Level Processing with Euclid and WFIRST We have now established a Tri-Agency, Three-Project Working Group (TAG). The members are: Nigel Sharp (NSF), Kathy Turner and Eric Linder (DOE), Dominic Tenerelli and Linda Sparke (NASA), Steve Kahn (LSST), Rachel Bean (DESC), Jason Rhodes (Euclid), Neil Gehrels (WFIRST). There are two sub-working groups: Pixel-level processing, and cosmological simulations. There are three anticipated phases to this activity: An unfunded scoping phase , that occurred over the summer, where the two sub- working groups made a plan for investigation and estimated rough costs. We were supposed to report out at a meeting on Sept 21-22, but that has now been postponed. An R&D phase, jointly funded by all three agencies. A construction phase, where the software to enable the processing is written. An implementation phase, where the joint processing is accomplished. If this is implemented in the LSST processing pipeline, as we expect it to be, the cost increase is not likely to be significant, but is still non-negligible. Science Advisory Committee Tucson November 16, 2015 10
Joint Pixel Level Processing with Euclid and WFIRST Cooperation with Euclid requires special consideration, because, at present, most Euclid Consortium members will not have access to LSST data, and most Americans will not have access to Euclid data during the proprietary periods. Draft agreements have been generated on both sides of the Atlantic, but, to date, none has been found acceptable to both sides. We are now reforming a Euclid/LSST discussion group to try to work this, first by cooperatively developing the science case, and then an implementation plan. But this process will be drawn out, and we do not expect an agreement on a very short timescale. Science Advisory Committee Tucson November 16, 2015 11
