SETI HUBBLE PICTURE ADDS TO PLANET-MAKING RECIPE (STScI-PR99-21)


Larry Klaes (lklaes@bbn.com)
Thu, 03 Jun 1999 11:27:59 -0400


>Date: Wed, 02 Jun 1999 09:05:09 -0400 >From: HST News Release <hst-news@stsci.edu> >X-Mailer: Mozilla 4.07 [en] (WinNT; I) >To: pio@stsci.edu >Subject: HUBBLE PICTURE ADDS TO PLANET-MAKING RECIPE (STScI-PR99-21) >Sender: owner-pio@stsci.edu > >EMBARGOED UNTIL: 12:30 pm (CDT)/1:30 pm (EDT) June 2, 1999 > >CONTACT: Donna Weaver > Space Telescope Science Institute, Baltimore, MD > (Phone: 410-338-4493) > (E-mail: dweaver@stsci.edu) > > Carol Grady > Goddard Space Flight Center, Greenbelt, MD > (E-mail: cgrady@echelle.gsfc.nasa.gov) > >PRESS RELEASE NO.: STScI-PR99-21 > > >HUBBLE PICTURE ADDS TO PLANET-MAKING RECIPE > >How do you cook up a planetary system? Astronomers can rattle off the >primary ingredients: gas, dust, and ice. They have seen the prepared >dish: our solar system. Now a detailed image of a developing star taken >by NASA's Hubble Space Telescope is helping them write the recipe. > >A visible-light image, taken with Hubble's Space Telescope Imaging >Spectrograph, reveals clumps of material in a circumstellar disk of gas >and dust swirling around a 2- to 4-million-year-old star called AB >Aurigae. These clumps, also composed of dust and gas, may >represent the seeds of planet formation. Studying developing stars in >the 1- to 10-million-year-old age range, such as AB Aurigae, could >provide an evolutionary missing link in the planet formation process. > >"These observations suggest that the transition from gas and dust disks >to debris disks with planets occurs around stars that are 1 to 10 >million years old," explains Carol Grady of the National Optical >Astronomy Observatories, working at the NASA Goddard Space Flight Center > >in Greenbelt, Md. "We have seen the beginning and the end of the planet >formation process. Recent Hubble telescope observations have shown >protoplanetary disks encircling young stars up to 1 million years old >and planetary disks surrounding more mature stars around 8 to 20 million > >years old. Now we want to see what is happening in the middle." > >Grady will discuss her findings at a press conference at 12:30 p.m. CDT >(1:30 p.m. EDT) June 2 at the summer meeting of the American >Astronomical Society in Chicago, Ill. > >Although the astronomer and her team haven't spied any planets in the >disk, the features they have seen intrigue them. > >"We don't see any evidence of unseen large bodies sweeping out dust >lanes," Grady says. "But we have seen unprecedented structure in the >dust clouds, suggesting that material is beginning to clump together in >a process which could form planets in the next few million years." > >The smallest clumps visible in this false-color image are near the >limits of the telescope's resolution. All the clumps are extremely >large: 1.3 to 3 billion miles (2 to 5 billion kilometers) wide or 14 to >32 times Earth's distance from the Sun. They also reside much farther >away from AB Aurigae than Pluto, our outermost planet, does from the >Sun. The largest clump, for example, is about 32 billion miles (51 >billion kilometers) away. This distance is equivalent to 88 times >Pluto's distance from the Sun. > >"Similar features haven't been seen in the disks surrounding younger, >300,000-year-old to 1-million-year-old, stars," Grady says. "In those >younger stars, we don't see as much structure as in AB Aurigae. Star >systems a bit older than AB Aurigae have cleared lanes or zones >suggesting that large planets have developed. The AB Aurigae image, >together with the other Hubble telescope studies, suggests that the >transition from a protoplanetary disk to a system with planets occurs >sometime after 2 to 4 million years, but before 8 million years." > >AB Aurigae, about 2.4 times more massive than the Sun, resides 469 >light-years from Earth in the constellation Auriga. Its circumstellar >disk is extremely wide, at least 121 billion miles (194 billion >kilometers). Thirty of our solar systems would fit inside it. The disk >is slightly larger than the nearby and better-studied Beta Pictoris >system. > >Normally, probing the material in a circumstellar disk is difficult >because the glare of the central star overpowers the feeble reflected >light from the dusty disk. To overcome this powerful light, Grady and >her team used the imaging spectrograph's coronograph, which blocks the >light from the star to create an artificial eclipse. > >Grady admits she needs more information on developing stars in order to >draw any conclusions on planet formation. That's why she and the Space >Telescope Imaging Spectrograph team have mapped out a two-year survey to > >study young, bright, nearby stars in the 1- to 10-million-year age >range. > >"Astronomers are searching for answers to planet formation," Grady >explains. "For example, is planet formation common? "How, when, and >where do planets form? And what role does a star's environment and size >play in planet formation?" > >AB Aurigae has been a popular target. The team selected this star >because of previous observations by ground- and other space-based >telescopes. Ground-based observations in millimeter wavelengths had >shown that the star has a large gas and dust disk; space- and >ground-based infrared studies had suggested that the disk material >extends in very close to the star, much farther than the imaging >spectrograph can see. > >The team plans further observations of AB Aurigae to search for comets. >Finding comets would mean that some of the clumps of dust and gas have >coalesced to form solid bodies at least a half-mile (1-kilometer) wide. >The astronomers will use the imaging spectrograph and NASA's soon-to-be >launched Far Ultraviolet Spectrograph Explorer to hunt for them. > >This research was supported by a NASA grant to the National Optical >Astronomy Observatories (NOAO). NOAO is operated by the Association of >Universities for Research in Astronomy (AURA), Inc., under cooperative >agreement with the National Science Foundation. > >The Space Telescope Science Institute is operated by AURA under contract > >with NASA's Goddard Space Flight Center in Greenbelt, MD. The Hubble >Space Telescope is a project of international cooperation between NASA >and the European Space Agency (ESA). > >- end - > >NOTE TO EDITORS: Image files and a photo caption are available at: >http://oposite.stsci.edu/pubinfo/pr/1999/21 and via links in >http://oposite.stsci.edu/pubinfo/latest and >http://oposite.stsci.edu/pubinfo/pictures. > >Higher resolution (300 dpi JPEG and TIFF) image files are available at >http://oposite.stsci.edu/pubinfo/pr/1999/21/extra-photos.html > >********************************** > >PHOTO CAPTION: > >EMBARGOED UNTIL: 12:30 p.m. CDT (1:30 p.m. EDT) June 2, 1999 > >PHOTO NO.: STScI-PRC99-21 > > >HUBBLE PICTURE ADDS TO PLANET-MAKING RECIPE > >NASA's Hubble Space Telescope has snapped a nearly face-on view of a >swirling disk of dust and gas surrounding a developing star called AB >Aurigae. The Hubble telescope image, taken in visible light by the Space > >Telescope Imaging Spectrograph, shows unprecedented detail in the disk, >including clumps of dust and gas that may be the seeds of planet >formation. > >Normally, a young star's bright light prevents astronomers from seeing >material closer to it. That's why astronomers used a coronograph in >these two images of AB Aurigae to block most of the light from the star. > >The rest of the disk material is illuminated by light reflected from the > >gas and dust surrounding the star. > >The image on the left represents the best ground-based coronographic >observation of AB Aurigae. Paul Kalas of the Space Telescope Science >Institute took the image with the University of Hawaii's 2.2-meter >telescope. The telescope's coronograph eclipsed a 33.5-billion-mile >(53.6-billion-kilometer) area centered on the star. This area is nine >times larger than our solar system. The picture shows that the star >resides in a region of dust clouds - the semicircular-shaped material to > >the left of the star. > >The Hubble telescope image on the right shows a windowpane-shaped >occulting bar -- the dark bands running vertically through the middle of > >the image and horizontally across the upper part of it. The occulting >bar covers the innermost part of the disk and star, about 7.1 billion >miles (11.5 billion kilometers) or 1.4 times our solar system's >diameter. The diagonal lines are the remnants of the diffraction spikes >produced in Hubble telescope images of bright stars. > >The disk is extremely wide: its diameter is roughly 1,300 times Earth's >distance from the Sun. The disk material seen in this image is at a >distance equivalent to well beyond Pluto's orbit. One faint background >star is visible at 5 o'clock. > >The star's disk shows a wealth of structure, with bright spiral-shaped >bands from 9 o'clock to 6 o'clock and closer to the star from 12 o'clock > >to 3 o'clock. The outermost of these bands are seen in the ground-based >image. The imaging spectrograph data show that these bands are >themselves composed of numerous smaller bands. The smallest features >include some bright knots of material to the left of the star. These >knots are close in size to the resolution limit of the Hubble telescope >and have diameters 1.3 to 3 billion miles (2 to 5 billion kilometers) >wide or 14 to 32 times Earth's distance from the Sun. The brightest knot > >is at 9 o'clock. > >The image was taken Jan. 23 and 24, 1999. False colors were used to >bring out details in AB Aurigae's disk. The wavelength range is 2,000 to > >10,100 Angstroms. > >Credit: C.A. Grady (National Optical Astronomy Observatories, NASA >Goddard Space Flight Center), B. Woodgate (NASA Goddard Space Flight >Center), F. Bruhweiler and A. Boggess (Catholic University of America), >P. Plait and D. Lindler (ACC, Inc., Goddard Space Flight Center), M. >Clampin (Space Telescope Science Institute), and NASA. > >The ground-based image is courtesy of P. Kalas (Space Telescope Science >Institute). > >



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