Astronomy Picture of the Day 02-21-04

Explanation: While stirring a morning cup of coffee and thinking cosmic thoughts many astronomers would glance at this Hubble Space Telescope image of spiral galaxy NGC 4622 and assume that the galaxy was rotating counterclockwise in the picture. One hundred million light-years away in the constellation Centaurus, NGC 4622's gorgeous outer spiral arms, traced by bright bluish star clusters and dark dust lanes, should be winding up like ... well, like swirls in a cup of coffee. But a closer look at this galaxy reveals that a pronounced inner spiral arm winds in the opposite direction. So which way is this galaxy rotating? Evidence combining ground-based spectroscopy and the sharp Hubble image data surprisingly indicates that the galaxy is likely rotating clockwise in the picture, its outer spiral arms opening outward in the direction of rotation. There are further indications that a past collision with a smaller companion galaxy has contributed to NGC 4622's bizarre rotational arrangement of spiral arms, essentially unique among known large spiral galaxies.

Large planetoid found beyond Pluto
ASTRONOMY NOW report
Posted: February 20, 2004

A new object located by the Near Earth Asteroid Tracking (NEAT) survey on February 17 and found in images by Mike Brown (Caltech), Chad Trujillo (Gemini Observatory) and David Rabinowitz (Yale), may be the largest object discovered in the solar system since Pluto in 1930.


Image credit: NEAT / JPL / NASA

2004 DW, to give its official designation, lies 2.4 billion km (1.5 billion miles) farther away than Pluto, placing it some 46 astronomical units (a.u.) from the Sun.

It belongs to a group known as the Kuiper Belt objects (KBOs), thousands of which are believed to have diameters larger than 100 km and lie in orbits that extend from Neptune (30 a.u.) out to 50 a.u. KBOs represent the primitive remnants of the early accretion phase of the solar system and are composed of ice and rock.

Given its distance, and assuming an albedo of about 9%, the diameter of 2004 DW is reckoned to be about 1,600 km (1,000 miles). If confirmed by subsequent measurements, it is considerably larger than a similar object named Quaoar (1,250 km) discovered in the summer of 2002. By comparison, Pluto is about 2,300 km in diameter.


Image credit: Chad Trujillo

Further observations are needed to refine the orbit, but it has already been located on images taken in 2002. Initial indications are that it is a 'Plutino' — a Kuiper Belt object with an orbit similar to that of Pluto. Curiously, the longitude of 2004 DW's perihelion is also close to that of Pluto.

Observers wishing to view the new object in backyard telescopes against the constellation backdrop of Hydra may be disappointed: its visual magnitude is currently +19.2.

We will bring you more on this story as it develops

More on the newly-discovered Kuiper Belt object:

Planetoid found in Kuiper Belt, maybe the biggest yet
CALIFORNIA INSTITUTE OF TECHNOLOGY NEWS RELEASE
Posted: February 20, 2004

Planetary scientists at the California Institute of Technology and Yale University on Tuesday night discovered a new planetoid in the outer fringes of the solar system.

The planetoid, currently known only as 2004 DW, could be even larger than Quaoar -- the current record holder in the area known as the Kuiper Belt -- and is some 4.4 billion miles from Earth.

According to the discoverers, Caltech associate professor of planetary astronomy Mike Brown and his colleagues Chad Trujillo (now at the Gemini North observatory in Hawaii), and David Rabinowitz of Yale University, the planetoid was found as part of the same search program that discovered Quaoar in late 2002. The astronomers use the 48-inch Samuel Oschin Telescope at Palomar Observatory and the recently installed QUEST CCD camera built by a consortium including Yale and the University of Indiana, to systematically study different regions of the sky each night.

Unlike Quaoar, the new planetoid hasn't yet been pinpointed on old photographic plates or other images. Because its orbit is therefore not well understood yet, it cannot be given an official name.

"So far we only have a one-day orbit," said Brown, explaining that the data covers only a tiny fraction of the orbit the object follows in its more than 300-year trip around the sun. "From that we know only how far away it is and how its orbit is tilted relative to the planets."

The tilt that Brown has measured is an astonishingly large 20 degrees, larger even than that of Pluto, which has an orbital inclination of 17 degrees and is an anomaly among the otherwise planar planets.

The size of 2004 DW is not yet certain; Brown estimates a size of about 1,400 kilometers, based on a comparison of the planetoid's luminosity with that of Quaoar. Because the distance of the object can already be calculated, its luminosity should be a good indicator of its size relative to Quaoar, provided the two objects have the same albedo, or reflectivity.

Quaoar is known to have an albedo of about 10 percent, which is slightly higher than the reflectivity of our own moon. Thus, if the new object is similar, the 1,400-kilometer estimate should hold. If its albedo is lower, then it could actually be somewhat larger; or if higher, smaller.

According to Brown, scientists know little about the albedos of objects this large this far away, so the true size is quite uncertain. Researchers could best make size measurements with the Hubble Space Telescope or the newer Spitzer Space Telescope.

The continued discovery of massive planetoids on the outer fringe of the solar system is further evidence that objects even farther and even larger are lurking out there. "It's now only a matter of time before something is going to be discovered out there that will change our entire view of the outer solar system," Brown says.

The team is working hard to uncover new information about the planetoid, which they will release as it becomes available, Brown adds. Other telescopes will also be used to better characterize the planetoid's features.

Disclaimer: Opinions posted on Free Republic are those of the individual posters and do not necessarily represent the opinion of Free Republic or its management. All materials posted herein are protected by copyright law and the exemption for fair use of copyrighted works.