Solar System Science with the SDSS

Robert Lupton

Zeljko Ivezic

Serge Tabachnik

Mario Juric

Jim Gunn

Jill Knapp

Michael Strauss

Princeton, June 2002

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A 2.2’ × 1.9’ piece of sky (0.2s)

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Stars (and galaxies) lie in well-defined parts of colourn space.

When searching for quasars, we are interested in the ‘outliers’,

the ones that don’t behave.

All the stars detected in about 2.5 square degrees of sky;

yellow-red colour v. red-infrared colour

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Not all weird-coloured objects are at cosmological distances.

The images map the i-r-g filters to RGB. The data is taken in

the order riuzg, i.e. GR··B

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Major Asteroid Surveys:

• Mc Donald Survey (Kuiper et al. 1958): 1000 asteroids

(m<16.5, 1,200 deg2)

• Palomar-Leiden Survey (van Houten et al. 1970): 2000 aster-

oids (m<20, 200 deg2)

• Spacewatch (Gehrels et al. 1991): 60,000 asteroids (m<21,

4,000 deg2)

• SDSS: >100,000 asteroids (m<21.5, 10,000 deg2) in five bands

SDSS measured ∼10 times more asteroid colors than all previous

surveys together (the largest previous multi-color survey: ECAS,

Zellner et al. 1985, with 600 objects)

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SDSS Asteroid Observations

• Moving objects must be efficiently found to prevent the con-

tamination of quasar candidates (and other objects with non-

stellar colors)

• Detected as moving objects with a baseline of only 5 minutes

• The sample completeness is 90%, with a contamination of 3%

• The velocity errors 2-10%, sufficient for recovery within a few

weeks

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Main SDSS Asteroid Results

• A measurement of the main-belt asteroid size distribution to

a significantly smaller size limit (< 1 km) than possible before

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SDSS Sensitivity for Detecting Moving Objects

SDSS can detect a 100-mile object beyond Neptune, and a 100-

yard object in the main asteroid belt

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Main SDSS Asteroid Results

• A measurement of the main-belt asteroid size distribution to

a significantly smaller size limit (< 1 km) than possible before

• Discovery of a break in the size distribution at D ∼ 5 km

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COMPARISON OF ASTEROID SIZE DISTR� IBUTION: OBSERVATIONS AND MODELS

The asteroid size distribution (Davis 2002, in Asteroids III).

SDSS results:1) Extended the observed range to ∼300m2) Detected the second break at ∼5 km

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Main SDSS Asteroid Results

• A measurement of the main-belt asteroid size distribution to

a significantly smaller size limit (< 1 km) than possible before

• Discovery of a break in the size distribution at D ∼ 5 km

• A smaller number of asteroids compared to previous work:

the number of asteroids with diameters larger than 1 km is

about 0.75 million

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1 101 10

The impact rate for D>1 km: once in a million years

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Main SDSS Asteroid Results

• A measurement of the main-belt asteroid size distribution to

a significantly smaller size limit (< 1 km) than possible before

• Discovery of a break in the size distribution at D ∼ 5 km

• A smaller number of asteroids compared to previous work:

the number of asteroids with diameters larger than 1 km is

about 0.75 million

• The distribution of main-belt asteroids in 4-dimensional SDSS

color space is strongly bimodal (rocky S-type and carbona-

ceous C type asteroids)

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The colours of a sample of known asteroids observed by SDSS

(a∗ is basically g − r)14

Main SDSS Asteroid Results

• A measurement of the main-belt asteroid size distribution toa significantly smaller size limit (< 1 km) than possible before

• Discovery of a break in the size distribution at D ∼ 5 km

• A smaller number of asteroids compared to previous work:the number of asteroids with diameters larger than 1 km isabout 0.75 million

• The distribution of main-belt asteroids in 4-dimensional SDSScolor space is strongly bimodal (rocky S-type and carbona-ceous C type asteroids)

• A bimodality is also seen in the heliocentric distribution ofasteroids: the inner belt is dominated by S type asteroidscentered at R ∼ 2.8 AU, while C type asteroids, centered atR ∼ 3.2 AU, dominate the outer belt.

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How do we know this? We cannot estimate orbits from our data.

• We cannot estimate orbits, but we can get (crude) distances

from the apparent motion of our asteroids

• We can use catalogues of known asteroids, and find them in

SDSS imaging data.

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The semi-major axis v. (proper) inclination of a sample of known

asteroids detected by SDSS

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The semi-major axis v. (proper) inclination of a sample of known

asteroids detected by SDSS

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The osculating inclination vs. semi-major axis diagram.

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Although optimized for Extragalactic science,

SDSS is significantly contributing toSolar System science

Princeton, June 2002

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A fast-moving asteroid.

The images map the i-r-g filters to RGB. The data is taken in

the order riuzg, i.e. GR··B

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