ISS astronaut Ron Garan photographed this Perseid over northern China on August 13, 2011.
Case studies:
Impact of 2008 TC3 [2008 Oct 7]
News:
May 04, 2009 - ASIMA mission was not selected for funding in the 2008 SALMON proposal round. Instead, the funding was allocated to two instruments that add to Mars and Mercury missions [more here] . We congratulate the investigators and instrument team for the LaRa and Strofio projects. We plan to resubmit the ASIMA mission for this fall's SALMON and/or Discovery calls.
March 26, 2009 - Recovery of fragments from the impact of 2008 TC3 announced. More here.
March 23, 2009 - ASIMA mission presented in a poster at the 40th Lunar and Planetary Science Conference, Houston, Texas.
December 01 - ASIMA small satellite mission proposal submitted to NASA.
October 29 - Meeting at NASA Ames Research Center. Discussion of technical aspects of the proposed mission.
October 17 - Visit to Ball Aerospace Corporation. Discussion of technical aspects of the proposed mission.
October 08 - Ames Research Center ASIMA kick-off meeting
October 06 - For the first time, a small (2-3 meter sized) asteroid was discovered in space on approach to Earth, just before hitting the Earth. More here.
Septemer 29 - The ATV-1 "Jules Verne" Multi-Instrument Aircraft Campaign successfully deployed ESA's "SPOSH" camera, an instrument designed for visual imaging of meteors from space, from two research aircraft. The cameras provided accurate astrometric information from two perspectives on the position of ATV during entry.
July 16 - Concept evaluation at the conference Asteroids Comets Meteors 2008.
Meteors observed from space: Composite of 1997 Leonid shower meteors in 1-second long exposures with the widefield camera of the MSX satellite. This camera captured -1 magnitude and brighter meteors.
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Principle of slit-less spectroscopy: each point of light creates a spectrum left and right of the meteor, the moving meteor creates a range of spectra for different heights. This example shows the reentry of ESA's ATV.
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Mission concept:
1. The girl's name Asima \a-si-ma\ is of Arabic origin, and its meaning is "guardian, protector".
2. A sanskrit word meaning "beyond boundaries".
In recent years, a host of spacecraft were flown to asteroids (NEAR, Deep Space 1, Cassini, Hayabusa, Dawn) and comets (Ice, Giotto, Deep Impact, STARDUST, and Rosetta). Despite the wealth of knowledge that is returned by these spacecraft on the chemical composition and physical structure of individual primitive bodies in our solar system, the bulk content of (non-volatile) carbon compounds in comets remains mostly unknown. Carbon compounds are important for the origin of life and are a sensitive probe of physical and chemical processes in the solar nebula at the time of formation.
Primitive bodies are by definition un-equilibrated, nor homogenised, a random product of nebular accretion processes. They are not a predictable geochemical system. They represent grab bag samples of the solar nebula, that is itself a highly dynamic system. To sample more than a few comets or asteroids via individual space missions is not yet an option.
Most information about comets and asteroids was learned from ground-based telescopic observations. Unfortunately, the bulk of carbon is in a 'tar'-like material that can not be measured in the gas phase of a comet's tail.
In order to measure carbon in a comet, we would need to destroy a small sample into its atomic elements. That is what meteors do naturally. Meteor spectroscopy, a form of "impact-induced breakdown spectroscopy", can measure the content of carbon relative to the metal atoms of iron and magnesium. Meteor showers trace to known comets, for example comet 109P/Swift-Tuttle, which is responsible for the Perseid shower. By letting the comet debris come to Earth, an Earth-bound satellite could visit up to ten different comets.
Earth's atmosphere protects us from harmfull UV light. But that sunscreen also prevents us from measuring the carbon content of meteors and fireballs from the ground. Carbon atoms radiate brightly only in the ultra-violet. From space, that sun screen is much less severe.
Earth as seen from a satellite at an altitude of 780 km.
To measure the carbon atom line emission requires relatively bright fireballs (about -5 magnitude and up). From 800 km altitude, 5 percent of the Earth's surface is visible at any given time. That is a much bigger area than covered by past and present ground-based fireball networks and provides a good detection rate for meteor shower fireballs caused by sub-meter and meter-sized asteroids and comets (when they are this small, all objects will look "star-like").
Relative scales of a typical target asteroid compared to a human being, and of asteroid 2008 TC3 compared to asteroid Itokawa and the International Space Station. These are the smallest worlds in our solar system. They are on a human scale. You could wrap your arms around it. They should still contain most of their non-volatile carbon compounds, the bulk of all carbon in the parent comet.
Very course information on the azimuthal direction of the meteor trajectory (from imaging) and its penetration depth (from extinction) will be used to identify to what meteor shower the fireball belongs. Each shower samples a unique parent body (see sidebar).
We plan to provide rapid information on the position and brightness of each meteor, as soon as data are downloaded from the satellite, so that ground-based observing teams could follow up by collecting video and still images of the fireball taken by observers on the ground.
ASIMA is a small instrument package that would be deployed as part of a larger satellite, for example on one of the Iridium satellites, at an altitude of 800 - 1000 km. It consists of three nadir-looking cameras, using the same tried and proven imaging technology.
If funded, this will be the first satellite dedicated to the study of meteors. What makes this mission different from others is that the whole visible part of the Earth is imaged in staring mode, not by a narrow-field scanner, with a transmission grating in front of the lens for instantaneous spectroscopy over the whole wavelength range.
UV photometer: One camera is operated as a photometer, an imaging camera (no grating) with rapid readout (370 Hz) and only 256 x 256 pixel resolution. This camera will be operated at solar blind wavelengths of 180-185 nm, where meteors radiate strongly, in order to filter out most of the auroral emissions. It is the primary means of detecting meteors (transient events lasting a few seconds with a slow ramp-up time compared to that of lightning).
UV spectrograph:Two cameras are coated to be sensitive to UV light in the range 160 - 290 nm (= solar blind) and equipped with a UV transparent lens with a 130 degree field of view. One is a large 1000 x 1000 pixel camera that takes relatively long exposures (1 per second) of the Earth. A transmission grating will create slit-less spectra with a resolution of better than 2 nm/pixel. Analysis of the UV images will provide a backup means of detecting meteor events.
Visible camera: A third camera is operated at visible wavelengths in the range 300 - 800 nm and equipped with a transmission grating for optical spectroscopy. Images are recorded in a buffer at a rate of 20 Hz, but only those images are downloaded that coincide with a meteor detection in the ultraviolet.
If approved, this mission would deploy in the 2012-2015 timeframe for a period of 2-3 years.
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