 |
|||||||||||||||||||||
| |||||||||||||||||||||
|
Dysnomia, a moon of Eris, was discovered on September 10, 2005. The discovery was made using the Laser Guide Star Adaptive Optics (LGS AO) system at the W.M. Keck Observatory. Images were taken at infrared wavelengths (2.1 microns) using the NIRC2 imaging camera over a period of 40 minutes. Dysnomia is located to the right of Eris in the picture.
As the earth turns, Eris, like all bodies in our solar system, appears to move across the sky at a different rate to distant stars. We know that the object is a moon of Eris because it follows Eris across the sky. By contrast, a star would appear to remain fixed. When the images are processed, the background stars appear to streak across the sky while Eris's companion does not. From these observations, we can say that Eris is 60 times brighter than Dysnomia. More observations, taken in August-October, 2006, have yielded data from which an orbit Dysnomia can be calculated. From the orbital period and semi-major axis (approximately the average distance between Eris and Dysnomia), it is possible to determine the mass of Eris and confirm that it is more massive than Pluto. A science article on the discovery was submitted to the Astrophysical Journal on October 2, 2005 and published on March 1, 2006. The article can be accessed here. Additional information is also available from Mike Brown's Dysnomia website.
|
|
Eris and Dysnomia
In September 2006, the International Astronomical Union granted "dwarf planet" status to the body officially known as 2003 UB313 and accepted the recommendation of the names Eris and Dysnomia proposed by Mike Brown. These objects were previously nicknamed Xena and Gabrielle, from the TV series, Xena: Warrior Princess. In Greek mythology, Eris is the goddess of chaos, an apt name for a body that has caused so much strife in forcing a new definition for what a planet is. Dysnomia is the daughter of Eris and the daimon of lawlessness, which is also a play on the actress who played Xena in the TV series, Lucy Lawless.
Gabrielle and Xena
|
Laser Guide Star Adaptive Optics
|
Light from stars is distorted by atmospheric turbulence. These distortions cause stars to appear to twinkle when viewed with the naked eye. Astronomers have been battling the effect of atmospheric turbulence since the advent of the telescope. On a very large telescope like those at Keck Observatory, the atmosphere reduces the level of detail by a factor of 10-100, depending on the wavelength (the color) at which the observations are carried out.
A new technology called adaptive optics (AO) is able to correct for these distortions. At the heart of AO is a deformable mirror that warps like a potato chip. Light is distorted by the atmosphere and undistorted by the deformable mirror, resulting in crisp images of the object being studied. The atmospheric distortions, called the wavefront, are measured as fast as 1000 times per second using a wavefront sensor. The main difficulty is that the wavefront sensor requires a bright star to make the wavefront measurement. Since most of the sky does not contain a sufficiently bright star, astronomers were very limited in the regions of the sky where they could use AO. To avoid this problem, the AO system at Keck Observatory is equipped with a laser guide star (LGS), which is able to create its own star anywhere in the sky! The Keck Observatory AO system has been used to capture a variety of beautiful images, some of which can be viewed in the AO image gallery. More information about the LGS AO system can be found in the LGS AO website. |
Linear scale image of a star with LGS AO off and on
|
Bright Kuiper Belt Objects
|
|
|
| Pluto and Charon | Easter Bunny | Santa and Rudolph |
| These images were all taken using the Keck Observatory LGS AO system. | ||
|
The Kuiper Belt is a region in the Solar System beyond the orbit of Neptune. Until the discovery of Eris (68 AU from the sun), Pluto was the biggest known Kuiper Belp Object (KBO). There are four KBOs that are bright enough that they can be imaged with the Keck Observatory LGS AO without relying on a bright enough star being close to the KBO by coincidence. In order of decreasing apparent brightness, they are Pluto, Easter Bunny (2005 FY9), Santa (2003 EL61) and Eris. Pluto has a moon called Charon, which was discovered in 1978. In addition, the discovery of two new, very faint satellites of Pluto was announced on October 31, 2005 by NASA scientists. We found two moons around Santa: the brightest one, at 11 o'clock, is nicknamed Rudolph. On November 29, 2005, we announced the discovery of the second moon, which can be seen directly below the primary KBO. Initially, we believed that it was a background star since it did not appear in all the observations of Santa! However, the orbit of this second satellite around Santa is consistent with the mass estimate for Santa obtained from the orbit of Rudolph. |
The Scientists and Engineers
Mike Brown is a professor of astronomy at Caltech who has been on the hunt for KBOs with a great deal of success. In addition to Eris, Easter Bunny and Santa, his program has also uncovered the existence of Sedna, Quaoar and 2004 DW. His collaborators are Chad Trujillo at Gemini Observatory and David Rabinowitz at Yale University. Mike Brown suggested Santa, Easter Bunny and Eri as possible engineering science targets during the commissioning period of the Keck Observatory LGS AO system.Three Keck Observatory scientists, Antonin Bouchez (now at Caltech), David Le Mignant and Marcos van Dam, searched for and found companions around the KBOs. The remainder of the Keck Observatory LGS AO team that built the instrument is: Peter Wizinowich (lead), Randy Campbell, Jason Chin, Scott Hartman, Erik Johansson, Robert Lafon, David Le Mignant, Paul Stomski and Doug Summers. Additional support was provided by Jim Lyke, Al Conrad, Cynthia Wilburn, Christine Melcher and Ronald Mouser. The LGS was built by Deanna Pennington, Curtis Brown and Pamela Danforth at Lawrence Livermore National Laboratory.
|
|
For more information, please contact
Back
Keck Observatory Adaptive Optics Kuiper Belt Objects Personal Webpages Information and Outreach Contact
|