Amanda Gulbis

Amanda Gulbis became a PAL member in Fall 2003. She left in June 2008 to take an astronomer position at the Southern African Large Telescope (SALT), based in Cape Town. She maintains her collaboration with PAL as an MIT visiting scientist. Her interests include the following:

(i) predicting and observing stellar occultations by small bodies in the outer Solar System;

(ii) the physical and atmospheric characteristics of Pluto, Charon, and other KBOs;

(iii) high-speed, visible wavelength instrumentation.

She also has a lingering interest in dust dynamics near planetary surfaces.

Stellar Occultations

    Stellar occultations, or the light from a star being blocked as it passes behind a foreground object, provide significant information on bodies in the outer solar system. Observations of these events offer some of the highest spatial resolution data that is achievable from Earth (on the order of a few km at Pluto). Therefore, stellar occultations are employed to determine planetary diameters and to probe the temperature and pressure profiles of planetary atmospheres. These events can also lead to the discovery of features such as satellites, rings, and atmospheres.

     During a stellar occultation, the shadow created on the Earth is a function of the size of the body and its distance from the Earth. For the objects in which we are interested (particularly Pluto & Charon, Triton, and Kuiper Belt objects), the shadow is significantly smaller than the Earth's angular diameter. An observer must thus be in the right place at the right time to see the occultation. We spend considerable time and effort taking observations and performing astrometry (measuring object and star positions) in order to predict these events. We then use portable CCD camera systems, which can be taken all over the world and attached either to portable telescopes or to telescopes that are located in the predicted shadow path.

POETS (Portable Occultation, Eclipse, and Transit Systems)

POETS, packed into its two airline carry-on cases.

    In collaboration with our colleagues at Williams College, we have constructed a set of instruments called POETS that are optimized for visible-wavelength occultation observations. Each of these systems consists of a high-speed camera, an instrument control computer, and a GPS to trigger frames and establish accurate timing – all of which can be transported as carry-on luggage. The cameras contain back-illuminated CCDs, 512 x512 arrays of 16 micron pixels, with > 90% quantum efficiency, ~6 electrons read noise, and only 1.74 msec deadtime during frame transfer.

    To date, we have deployed POETS with great success: the 18 March 2007 occultation of P445.3 by Pluto observed from the southwestern U.S. (Person et al. and McCarthy et al., in prep), the 12 June 2006 occultation by Pluto of P384.2 observed from Australia and New Zealand (Elliot et al., 2007), and the 11 July 2005 occultation of C313.2 by Charon observed from South America (Gulbis et al., 2006 & Person et al., 2006). We are currently working on predicting stellar occultations by Kuiper Belt objects (KBOs), in order to determine object diameters and search for binaries and atmospheres. In addition, we plan to utilize POETS for other high-speed, observational applications, such as extrasolar planet transits.

    We recently constructed and mounted a POETS on NASA's 3-m Infrared Telescope Facility (IRTF) on Mauna Kea, Hawaii. See the IRTF POETS website for details and updates.

Characteristics of KBOs, Pluto and Charon

Images of KBO 2001QT297 from MagIC on the Clay 6.5-m Magellan telescope at Las Campanas Obs., observed 11 September 2004. (Roll cursor over image to show object motion.)

  The Kuiper Belt, a group of small objects having orbits from ~ 30 to 50 AU, is particularly fascinating because it is likely the least thermally modified region of the solar system and thus may contain a primordial population of objects. This is important because objects that are remnants from earlier times provide insight into the formation and evolution of the solar system. In addition, they provide clues for understanding planetary formation processes that are occurring around other stars. Pluto and Charon, while special because they were discovered long before other KBOs, are located in the Kuiper Belt (in a 3:2 resonance with Neptune).
     Our group has studied Pluto and Charon via stellar occultation observations. Through this work, we have tracked changes in Pluto's atmosphere (e.g. Elliot et al., 2007) and set stringent limits on the size and possible atmosphere of Charon (Gulbis et al., 2006 & Person et al., 2006). We have studied the Kuiper Belt by searching for new objects (as part of the Deep Ecliptic Survey) and performing dynamical analyses (e.g. Elliot et al., 2005). We have also investigated the relationship between KBO orbital dynamics and color through photometric observations with the Magellan 6.5-m telescopes at Las Campanas Observatory (Gulbis et al. 2006).

Dust dynamics near planetary surfaces

Particles of JSC-1 (lunar regolith simulant) levitating in a plasma sheath above a plate in the laboratory.

   Evidence of dust dynamics near surfaces in the solar system ranges from particles observed levitating above the lunar horizon by the Surveyor spacecraft to the more recently discovered dust ‘ponds’ on asteroid Eros. Such dust dynamics are most likely the result of interactions between charged dust particles and plasma sheaths above planetary surfaces.

    My thesis work involved experimental investigations of dust charging and dynamics near surfaces with sheaths and related the results to environments on the Moon, Eros, and Mercury. Thus I have a continuing interest in dust dynamics near the surfaces of bodies in the Solar System. For additional details, please see my publications on dust dynamics and/or the Univ. of Colorado's dusty plasma group.