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RSAA News of the Month: April 2004

Searching for the Rest of the Solar System
Two RSAA surveys find remnants of the early Solar System, near Earth and beyond Neptune

 

Near Earth
Story from Steve Larson (UA) and Rob McNaught & Gordon Garradd (RSAA)

The hunt for space rocks on a collision course with Earth has so far been pretty much limited to the Northern Hemisphere, but now astronomers have taken the search for Earth-threatening asteroids to southern skies. A new program using a refurbished telescope at the Australian National University's Siding Spring Observatory has produced its first discoveries of near-Earth asteroids (NEAs). NEAs are asteroids that pass near the Earth and may pose a threat of collision.

On March 29, 2004, the Siding Spring Survey (SSS) discovered its first two near-Earth asteroids. Astronomer Gordon Garradd detected them on images he obtained with the 0.5-meter Uppsala Schmidt telescope. Both objects were confirmed later that night by SSS partner Rob McNaught who was using the Siding Spring 40" telescope to refine orbits of other, known, NEAs.

First of the NEAs, designated 2004 FH29, is about 100m in diameter and has an orbit that comes close to Earth's orbit every 2.13 years. The second one, 2004 FJ29, is about 300 meters in diameter and is in an orbit that crosses Earth's every 46 weeks. Neither object poses a threat of colliding with the Earth.

Discovery images of 2004FH29 (left) and 2004FJ29 (right).

Asteroids, comets and TNOs are found by their movement across the sky.
Four images of the starfields are being blinked.
The NEAs are moving in the direction of the arrows.

The survey, a joint collaboration between the University of Arizona Lunar and Planetary Laboratory and the ANU's Research School of Astronomy and Astrophysics (RSAA), is designed to discover potentially hazardous near-Earth objects (NEOs). It is funded by NASA's Near-Earth Object Observation Program, charged with discovering and tracking 90% of the 1-km or larger NEOs with the potential to become impact hazards.

The Uppsala Schmidt telescope was built in the 1950s for Uppsala Observatory in Sweden, and was sited at Stromlo Observatory as the Uppsala Southern Station. Its task was to make wide field photographs of the southern sky, a region not observable from Sweden. Increasing light pollution from Canberra led to its relocation to Siding Spring in 1982. Despite its high quality optics, it gradually drifted into disuse because of its use of photographic plates rather than modern electronic cameras, its manual operation, and the presence on the mountain of the much larger 1.2m UK Schmidt telescope.

The 0.5m Uppsala Schmidt telescope at Stromlo, being dismantled for removal to Siding Spring,
being re-housed at Siding Spring, and as it is today after refurbishment for SSS.
Images: McNaught, Larson, and RSAA archives.
For more images of the Uppsala Schmidt, click here.

During the upgrade for SSS, the Uppsala was completely reconditioned and fitted with computer control, a large format (16Mpix) solid state detector array, and extensive support computers and software to detect objects moving against the background stars. The telescope commenced observing again in late March. The SSS builds upon telescope control and detector technology and software developed for the Catalina Sky Survey (CSS), which uses a similar Schmidt near Tucson, Arizona.

SSS is very important. Of the 11 NASA-supported telescopes searching for NEOs, it is the only one with a clear view of the entire southern sky. It is probable that some of the largest NEAs still remain undetected, only becoming visible when deep in the southern skies. Comet discoveries will also be an inevitable "byproduct" of the survey. As some of these also approach the Earth from time to time, they are part of the overall program of finding both threatening asteroids and comets.

The SSS plan is to use the 40-inch telescope to quickly confirm suspect asteroids detected with the Uppsala, freeing the smaller telescope to continue its searches. "Our confirmation strategy worked beautifully on our first try," McNaught said.

McNaught and Garradd currently operate the SSS. Commissioning was done with the assistance of the University of Arizona's Ed Beshore and Principal Investigator Stephen Larson. Commissioning a telescope is like commissioning a ship: You have to get all the parts working together, and adjust things so they perform as expected. "We actually achieved 'first light' last summer, with good images from the start," Larson said. Other members of the CSS team are Eric Christensen, Rik Hill, David McLean and Serena Howard.

Both SSS and CSS telescopes can detect objects as faint as 20th magnitude. This is close to the limit of sky brightness generated by scattered city lights (not such a problem at Siding Spring) and auroral glow that brightens Earth’s upper atmosphere.

For the latest results and information from SSS, click here.
For current information about Near Earth Objects, including their dates of closest approach to Earth and their distance from it at the time, click here.

 

Beyond Neptune
Story from Rachel Moody (RSAA)

In 1992 an almost forgotten field of astronomy was reawakened with the discovery of a small icy body orbiting the Sun beyond Neptune. It was quickly found that this object was the first of many so-called Trans-Neptunian Objects (TNO’s) forming a ring of debris beyond the orbit of Neptune. This ring has been named after the two astronomers who first predicted its existence, Edgeworth and Kuiper. The Edgeworth-Kuiper Belt is thought to contain most of the remnants left over from the formation of the solar system.

The importance of this region has been recently highlighted with the worldwide attention given to NASA's discoveries of TNOs Quaoar and Sedna, the largest bodies found in the solar system since Pluto, 74 years ago. These small “planetoids” are forcing astronomers to once again ask the question, what is a planet?

ANU's Research School of Astronomy and Astrophysics is taking part in the international search for new outer solar system bodies. The survey began in 2000, using the 1.3 m 'Great Melbourne Telescope'. The Southern Edgeworth-Kuiper Belt Survey was an ambitious program more than 10 times larger than any previous survey of its type, and the only one to be undertaken in the southern hemisphere.

The 50" ex-Great Melbourne Telescope before and after the firestorm of 18 Jan 2003.
For more images of the 50", click here.

The telescope and associated computers were destroyed in the January 2003 firestorm. Rachel Moody, the project leader, was offered the use of computing facilities at the University of Pennsylvania and moved there for a year to completely rebuild the survey software and analyse the data from the year of operation.

Using a unique strategy to detect these distant objects, Rachel successfully recovered three previously known, but lost, members of the belt and made three new TNO discoveries. These new minor planets almost double the number of large objects detected to date, with the largest rivaling the size of Quoaor.

Detection and confirmation images for two TNOs.

In each set the first image is a red light image of the target field,
the second is a red reference image of the same field taken at an earlier date,
the third is a blue target image and the fourth is a blue reference image.

The three rows of images are observations from different dates.
Because the TNOs are moving, the star fields are different on each row.
TNO candidates are the faint objects at the centre of the target fields, but are absent on the reference fields.

From observations on 3 dates, an approximate orbit for the TNO can be calculated and its status as an outer Solar System object confirmed.
Candidate 1 is a newly-discovered TNO. Candidate 2 could have been Rachel's first new TNO if the fire had not interrupted data processing.

The three candidates are currently being re-observed using the 40” telescope at Siding Spring Observatory, near Coonabarrabran NSW, to determine accurate positions for the next 10 years which will give astronomers worldwide the opportunity to observe these rare and mysterious objects.

The results of the survey are some of the most detailed and accurate measurements of the outer solar system. They will not only prove invaluable in our quest to probe what was once thought to be a barren region of space, but will help us to explore the link between the formation of our solar system and planetary systems around other stars.

Images: Moody and RSAA archives

For previous Monthly News items, click here.