13488( 2) - 26-Jun-2013 18:19:33 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 13488 Version: 2 Check-in Time: 26-Jun-2013 18:19:33 STScI Edit Number: 0 Title Using Hubble to Resolve Fundamental Discrepancies in the Surface Composition of the Asteroid (21) Lutetia ------------------------------------------------------------------------------------ Type Cycle GO 21 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Andrew J. Steffl Southwest Research Institute Y CoI: Dr. Harold A. Weaver The Johns Hopkins University Applied N Physics Laboratory CoI: Dr. S. Alan Stern Southwest Research Institute N CoI: Dr. Eric Robert Schindhelm Southwest Research Institute N ------------------------------------------------------------------------------------ Abstract (21) Lutetia is one of the largest asteroids in the main belt, with dimensions of 121x101x75 km along its principal axes of inertia. On July 10, 2010, the European Space Agency's Rosetta spacecraft passed within 3168 +/- 7.5 km of Lutetia's surface. However, even after the Rosetta flyby, fundamental uncertainties remain about the composition of Lutetia's surface. The primary reason for this is that from visible to millimeter wavelengths, Lutetia's reflectance spectrum is almost completely devoid of absorption features and contains nothing that can uniquely constrain its surface composition. The scientific literature is now split with about half advocating an enstatite chondrite composition and half a carbonaceous chondrite composition. Although these materials look similar in the visible/IR, they have markedly different appearances in the NUV. In addition, the FUV spectrograph on the Rosetta spacecraft identified a strong absorption edge in Lutetia's spectrum at 170nm. This could be indicative of plagioclase feldspar minerals or water ice. The presence of either of these materials is not expected on Lutetia's surface and would be a major discovery. However, it is not possible to confirm/rule out their presence using existing data--for that NUV spectra are required. We propose a focused, 4-orbit program to obtain the spectrum of Lutetia from 180-570nm using STIS/G230L and STIS/G430L. ------------------------------------------------------------------------------------ Observations Description ------------------------ The goal of this program is to obtain spectra of the asteroid (21) Lutetia from 180-570nm. Using our best estimate of Lutetia's spectrum--derived from FUV spectra by the Rosetta Alice spectrograph and ACS photometry--and the STIS and COS ETCs, we find that the STIS/G230L is more efficient than the COS/G230L. The predicted global count rate from the STIS ETC is 2460, well below the MAMA bright object limits. We will therefore operate the STIS NUV MAMA in TIME-TAG mode with a very conservative buffer time of 650s. Seen from Earth at opposition, Lutetia is about 0.075" in diameter, so it will appear only marginally larger than a point source. Thus, we will use the 52"x0.2" slit. Based on the results from the ETC, obtaining a SNR of 10 at 200 nm for a 2-pixel resel (3.2 A resolution) requires 7331s of integration time. In this phase II proposal, we obtain a total of 7830s. SNRs in excess of 100 will be achieved at wavelengths greater than ~260 nm. The STIS/G430L configuration 13488( 2) - 26-Jun-2013 18:19:33 - [ 2] provides a bridge between the NUV and visible, covering the wavelength range of 295-570 nm with high SNR. Since the Sun, and hence Lutetia, is significantly brighter in the visible than the NUV, we can obtain comparable SNRs in just 200s of total integration time using the STIS CCD and G430L grating (CR-SPLIT=3). The SNR is > 50 for all wavelengths > 310 nm. Real Time Justification ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- The length of the planned orbits (and amount of unused observing time, if any) should be re-checked in early 2014, when the orbit of HST becomes known. ------------------------------------------------------------------------------------ 13488( 2) - 26-Jun-2013 18:19:33 - [ 3] TARGET LIST Solar System Targets ------------------------------------------------------------------------------------------------------------------------------------ TARGET NUMBER: 1 TARGET NAME: ASTEROID-LUTETIA ------------------------------------------------------------------------------------------------------------------------------------ TARGET DESCRIPTION: ASTEROID The asteroid (21) Lutetia ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 1 TARGET POSITION LEVEL 2 TYPE=ASTEROID, A=2.434254224700, E=0.164545157839, I=3.063861842541, O=80.884245472306, W=250.213284373741, M=220.967267326744, EQUINOX=J2000, EPOCH=22-MAR-2014:00:00:00, EpochTimeScale=UTC ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 3 WINDOWS ------------------------------------------------------------------------------------------------------------------------------------ DATA COMMENTS V = 11.02 +/- 0.3 Ephemeris Center: EARTH ------------------------------------------------------------------------------------------------------------------------------------ 13488( 2) - 26-Jun-2013 18:19:33 - [ 4] Visit: 01 Visit Requirements: BETWEEN 17-MAR-2014:18:00:00 AND 27-MAR-2014:03:00:00 On Hold Comments: Additional Comments: For accurate determination of Lutetia's geometric albedo (defined as the reflectance at a phase angle of 0 deg) we require the phase angle correction to be < 30%. This constrains the observations to occur when Lutetia's phase angle is < 2.7 deg, when seen from Earth, which occurs between 2014 Mar 17-28. Although we can accept observations at any time during this window, we strongly prefer the visit be made as close to opposition (2014-Mar-22 11:00:00) as possible. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 ASTEROID-LU STIS/CCD ACQ F28X50LP MIRROR 1 .1 S (0.1 TETIA S) ------------------------------------------------------------------------------------------------------------------------------------ 2 ASTEROID-LU STIS/NUV TIME-TA 52X0.2 G230L 2376 BUFFER-TIME=650 1 2130 S TETIA -MAMA G (2130 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 ASTEROID-LU STIS/CCD ACQ F28X50LP MIRROR 1 .1 S (0.1 TETIA S) ------------------------------------------------------------------------------------------------------------------------------------ 4 ASTEROID-LU STIS/NUV TIME-TA 52X0.2 G230L 2376 BUFFER-TIME=650 1 2100 S TETIA -MAMA G (2100 S) ------------------------------------------------------------------------------------------------------------------------------------ 5 ASTEROID-LU STIS/CCD ACQ F28X50LP MIRROR 1 .1 S (0.1 TETIA S) ------------------------------------------------------------------------------------------------------------------------------------ 6 ASTEROID-LU STIS/CCD ACCUM 52X0.2 G430L 4300 CR-SPLIT=3 1 200.1 S TETIA (200.1 S) ------------------------------------------------------------------------------------------------------------------------------------ 7 ASTEROID-LU STIS/NUV TIME-TA 52X0.2 G230L 2376 BUFFER-TIME=650 1 1500 S TETIA -MAMA G (1500 S) ------------------------------------------------------------------------------------------------------------------------------------ 8 ASTEROID-LU STIS/CCD ACQ F28X50LP MIRROR 1 .1 S (0.1 TETIA S) ------------------------------------------------------------------------------------------------------------------------------------ 9 ASTEROID-LU STIS/NUV TIME-TA 52X0.2 G230L 2376 BUFFER-TIME=650 1 2100 S TETIA -MAMA G (2100 S) ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ ASTEROID-LUTETIA 1 STIS/CCD ACQ F28X50LP MIRROR none none none none 1 N/A ASTEROID-LUTETIA 2 STIS/NUV TIME-TA 52X0.2 G230L 2376 none none none none 1 N/A -MAMA G ASTEROID-LUTETIA 3 STIS/CCD ACQ F28X50LP MIRROR none none none none 2 N/A 13488( 2) - 26-Jun-2013 18:19:33 - [ 5] Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ ASTEROID-LUTETIA 4 STIS/NUV TIME-TA 52X0.2 G230L 2376 none none none none 2 N/A -MAMA G ASTEROID-LUTETIA 5 STIS/CCD ACQ F28X50LP MIRROR none none none none 3 N/A ASTEROID-LUTETIA 6 STIS/CCD ACCUM 52X0.2 G430L 4300 none none none 1 3 N/A ASTEROID-LUTETIA 6 STIS/CCD ACCUM 52X0.2 G430L 4300 none none none 2 3 N/A ASTEROID-LUTETIA 6 STIS/CCD ACCUM 52X0.2 G430L 4300 none none none 3 3 N/A ASTEROID-LUTETIA 7 STIS/NUV TIME-TA 52X0.2 G230L 2376 none none none none 3 N/A -MAMA G ASTEROID-LUTETIA 8 STIS/CCD ACQ F28X50LP MIRROR none none none none 4 N/A ASTEROID-LUTETIA 9 STIS/NUV TIME-TA 52X0.2 G230L 2376 none none none none 4 N/A -MAMA G 13488( 2) - 26-Jun-2013 18:19:33 - [ 6] Summary Form for Proposal 13488 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures 52X0.2, F28X50LP ------------------------------------------------------------------------------------------------------------------------------------ Configurations STIS/CCD, STIS/NUV-MAMA ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM, ACQ, TIME-TAG ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters BUFFER-TIME=650, CR-SPLIT=3 ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements BETWEEN 17-MAR-2014:18:00:00 AND 27-MAR-2014:03:00:00 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements G230L, G430L, MIRROR ------------------------------------------------------------------------------------------------------------------------------------ Target Names ASTEROID-LUTETIA ------------------------------------------------------------------------------------------------------------------------------------