Planetary Astronomy Late-morning Seminar for 2019-02-12

Series: Planetary Astronomy Late-morning Seminar
Date: Tuesday 12-Feb-2019
Time: 11:00-12:00
Location: CSS 1250
Speaker: Amaya Moro-Martin (STScI)
Title: 1I/'Oumuamua

1I/'Oumuamua is the first interstellar interloper that has been detected (Williams et al. 2017) and, even though it was the subject of an intense observational campaign, its brief visit left several key questions unanswered. One of them is the number density of free-floating 1I/'Oumuamua-like objects inferred from its detection frequency, an aspect that relates to 1I/'Oumuamua's origin. I will describe how this estimate is orders of magnitude larger than what would be expected from the ejection of planetesimals from circumstellar and circumbinary disks (Moro-Martín 2018), and also from the ejection of exo-Oort cloud objects under the effect of post-main sequence mass loss, stellar encounters, and the galactic tide, even when considering the large uncertainties involved in these calculations, like the size distribution of ejected bodies (Moro-Martín 2019a). Another open question is 1I/'Oumuamua's physical properties: observations with Spitzer could not detect its thermal emission, with the 3-sigma upper limit at 4.5 mm leading to an effective spherical radius of less than [49, 70, 220] m, for an albedo greater than [0.2, 0.1, 0.01] (Trilling et al. 2018), with an axis ratio of 6±1:1, making it unusually elongated (McNeill et al. 2018). And the other puzzle regarding 1I/'Oumuamua is its non-gravitational acceleration, a 30-sigma detection that has been interpreted as evidence of outgassing (Micheli et al. 2018). The newly released Spitzer results, however, imply a 3-sigma upper limit to the CO outgassing level that is four orders of magnitude lower than what would be required to support this outgassing scenario, unless one assumes relative volatile abundances that are very different from those found in comets. Bialy & Loeb (2018) have suggested that, rather than outgassing, the non-gravitational acceleration could be due to radiation pressure. According to these authors, this would require an area-to-mass ratio corresponding to the physical properties of a thin sheet 0.3--0.9 mm in width, suggesting that 1I/'Oumuamua represents a new class of thin interstellar material that is either produced naturally by an unknown process or artificially, like a lightsail. As an alternative to this scenario, I discuss whether a naturally-produced, mass fractal structure with a high area-to-mass ratio could contribute to a radiation-pressure-driven 1I/'Oumuamua (Moro-Martín 2019b).

For further information contact PALS coordinator Dr. Matthew Knight at or (301)-405-2629.


Special accommodations for individuals with disabilities can be made by calling (301) 405-3001. It would be appreciated if we are notified at least one week in advance.


Directions and information about parking can be found here.

This page was automatically generated on: 16-Jan-2019.