LCROSS Impact Briefing

Public Observation Campaign

The Mission Objectives of the Lunar Crater Observation and Sensing Satellite (LCROSS) include confirming the presence or absence of water ice in a permanently shadowed crater in the Moon's polar regions. The identification of water is very important to the future of human activities on the Moon. LCROSS will excavate the permanently dark floor of one of the Moon's polar craters with two heavy impactors in 2009 to test the theory that ancient ice lies buried there. The impact will eject material from the crater's surface and subsurface to create a plume that specialized instruments will be able to analyze for the presence of water (ice and vapor), hydrocarbons and hydrated materials.

Mission scientists estimate that the Centaur impact plume may be visible through amateur-class telescopes with apertures as small as 10 to 12 inches. As the mission progresses, this site will provide the general public, classrooms, and the amateur astronomy community details on how to observe the impact. The LCROSS mission will actively solicit images of the impact from the public. These images will provide a valuable addition to the archive of data chronicling the impact and its aftermath. This site will include a gallery of images received from both the public and professional communities.

You can read more about LCROSS on its main website.

How Can I Participate?

The LCROSS mission provides a rare and unique opportunity for the amateur community to contribute directly to the science of a NASA mission.

When the LCROSS Centaur upper stage impacts the south pole of the Moon on October 9, 2009 at approximately 4:30 a.m. PDT, the ejecta plume may be observable in 10” and larger telescopes for a few minutes after impact as the ejecta reaches sunlight above the target crater. Amateur astronomers that can take high-resolution images, video, spectra, etc. of the Moon will be able to contribute to the LCROSS mission.

Impact Details

Areas west of longitude 95°W in North America will have the Moon high in a dark sky to allow for observations of the impacts. The major observatories on Mauna Kea and Haleakala in Hawai’i have excellent viewing geometry, as do the many observatories on the west coast and in the American southwest.

Earth viewed from Lunar South Pole showing area of visibility at time of impact.
Graphic courtesy Project Pluto GUIDE 8.0

Impact Timing

The impact time is approximately 11:30 UT, or 4:30 a.m. PDT, 5:30 a.m. MDT and 6:30 a.m. CDT. The impact time will be known to within one second approximately nine hours before impact. The updated impact time will be posted online at http://www.nasa.gov/lcross.

Impact Location

The final target crater selection is CABEUS, identified in the photos below.

CABEUS is identified here by the symbols SP_C

Plume Characteristics

We expect the plume to extend approximately 10 km in height (mass weighted maximum vertical extent) and extending about 30 km across by the time it becomes too diffuse to observe. At its maximum predicted extent, the plume will be about 1/4 the apparent size of Jupiter as viewed through a telescope. The shape of the ejecta cloud resembles an 'upside down lampshade'.

The expected plume average brightness for the Centaur (first) impact event is 4-6 visual magnitudes per arcsec-squared (it's an extended object) in the first minute. However, observations are not trivial as the dust cloud will have a brightly lit Moon surface behind it, making it more difficult to see the dust cloud due to the poor contrast; bright dust against a bright Moon surface. The dust will polarize the scattered light but using polarimetery can help with the observation.

Visual Observations

Observations of the ejecta plume made visually rather than with a camera will have limited scientific value, although it may be interesting to note what size and type of telescope and magnification was needed to see the event.

Still Photography

Digital Single Lens Reflex (DSLR) cameras are ideal for plume imaging. A telescope/camera/projection lens combination that can produce an Effective Focal Length (EFL) of about 4,000 mm is suggested to give a good image scale. Exposures tests can be made well in advance of the impact date. The impact plume will be observed mostly against a bright lunar backdrop, so exposures used to record good lunar images should be able to image the plume. The plume is likely to be most easily observable during the first 30 seconds after impact as it rises above the darkened floor of the target crater. Photos taken in rapid sequence can later be turned into AVI or animated GIF files.

Video Photography

Video imaging is generally more difficult, but good low-light video cameras are commercially and easily available. C-mount cameras are best, which have no intervening lens and can be used prime-focus on a telescope with an appropriate C-mount/T-adapter to the telescope’s focusing tube. Black and white cameras are much more sensitive than color cameras. Low-light cameras are excellent choices, but cameras with variable gain and frame integrating features are far superior in imaging sensitivity and control. The small chip size of many of these cameras (1/3”) dictates an EFL of around 2,000mm or greater may be used.

CCD Imaging

Many advanced amateurs have Charge-Coupled Device (CCD) imaging equipment. Due to the relatively short exposures needed for plume imaging compared to what these cameras are designed for, auto-guiding and cooled detectors would not be necessary. Using CCDs would therefore be similar to imaging with a DSLR camera. CCD cameras can be calibrated, and therefore can provide much more detailed scientific information than either DSLR or video cameras. Tri-color imaging with CCD cameras is also possible, but usually requires a 'stationary' target due to the multiple exposures through different filters needed. The plume would 'smear' between exposures. However, color information could be an extra boon to the scientific community to warrant the effort of obtaining tri-color data.

Telescope Notes

Good, clean and well-aligned optics will be necessary to reduce scattered light. The plume will be very faint compared to the illuminated waning gibbous Moon, so any technique that can reduce stray light in your optical system should be used. If available, the tracking rate of the telescope mount should be set on LUNAR RATE to track the Moon more accurately.

Additional Information

A good discussion about several possible photographic techniques, possible plume visibility and interpreted plume dynamics by amateur astronomer Kurt Fisher can be found at: Kurt Fisher Impact Notes version 9-29 (14MB).

Pre-planning and obtaining sample exposures prior to impact are most important. Try out your equipment early. Several groups such as the International Occultation Timing Association (IOTA), Sky & Telescope, and LCROSS Google Groups pages have information on video techniques, cameras, timing methods, etc. The main LCROSS NASA website at http://www.nasa.gov/lcross will post any final pre-impact updates.

Specific help for advanced amateurs is available from astronomer Rick Baldridge at rickbaldridge@comcast.net.