Observations of Al, Fe and Ca(+) in Mercury's Exosphere

We report 5-(sigma) tangent column detections of Al and Fe, and strict 3-(sigma) tangent column upper limits for Ca(+) in Mercury's exosphere obtained using the HIRES spectrometer on the Keck I telescope. These are the first direct detections of Al and Fe in Mercury's exosphere. Our Ca(-) observation is consistent with that reported by The Mercury Atmospheric and Surface Composition Spectrometer (MASCS) on the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft

Observations of the Minor Species Al, Fe and Ca(+) in Mercury's Exosphere

We report the first detections of Al and Fe, and strict upper limits for Ca(+) in the exosphere of Mercury, using the HIRES spectrometer at the Keck I telescope. We report observed 4-sigma tangent columns of 1.5x10(exp 7) Al atoms per square centimeter at an altitude of 1220 km (1.5 Mercury radii (R(sub M)) from planet center), and that for Fe of 1.6 x 10 per square centimeter at an altitude of 950 km (1.4 R(sub M)). The observed 3-sigma Ca(+) column was 3.9x10(exp 6) ions per square centimeter at an altitude of 1630 km (1.67 R(sub M). A simple model for zenith column abundances of the neutral species were 9.5 x 10(exp 7) Al per square centimeter, and 3.0 x 10(exp 8) Fe per square centimeter. The observations appear to be consistent with production of these species by impact vaporization with a large fraction of the ejecta in molecular form. The scale height of the Al gas is consistent with a kinetic temperature of 3000 - 9000 K while that of Fe is 10500 K. The apparent high temperature of the Fe gas would suggest that it may be produced by dissociation of molecules. A large traction of both Al and Fe appear to condense in a vapor cloud at low altitudes

NIHTS: the near-infrared high throughput spectrograph for the Discovery Channel Telescope

NIHTS is a first-generation instrument now in use on Lowell Observatory’s Discovery Channel Telescope. It is a nearinfrared prism spectrograph of the BASS design featuring high throughput and low dispersion that is intended for observations of faint solar system and astrophysical objects over the YJHK spectral range. An unusual feature is its ability to observe simultaneously with the Large Monolithic Imager, an optical CCD camera, by means of a dichroic fold mirror. This is particularly valuable for time-variable targets such as Kuiper Belt Objects, asteroids, exoplanet transits, and brown dwarfs. We describe its design details and performance both in the lab and on the telescope

Haze in Pluto's atmosphere: Results from SOFIA and ground-based observations of the 2015 June 29 Pluto occultation

On UT 29 June 2015, the occultation by Pluto of a bright star (r′ = 11.9) was observed from the Stratospheric Observatory for Infrared Astronomy (SOFIA) and several ground-based stations in New Zealand and Australia. Pre-event astrometry allowed for an in-flight update to the SOFIA team with the result that SOFIA was deep within the central flash zone (~22 km from center). Analysis of the combined data leads to the result that Pluto's middle atmosphere is essentially unchanged from 2011 and 2013 (Person et al. 2013; Bosh et al. 2015); there has been no significant expansion or contraction of the atmosphere. Additionally, our multi-wavelength observations allow us to conclude that a haze component in the atmosphere is required to reproduce the light curves obtained. This haze scenario has implications for understanding the photochemistry of Pluto's atmosphere

Detection of Mercury's Potassium Tail

International audienceGround-based observations of Mercury's exosphere bridge the gap between the MESSENGER and BepiColombo missions and provide a broad counterpart to their in situ measurements. Here we report the first detection of Mercury's potassium tail in both emission lines of the D doublet. The sodium to potassium abundance ratio at 5 planetary radii down-tail is approximately 95, near the mid-point of a wide range of values that have been quoted over the planet's disk. This is several times the Na/K present in atmospheres of the Galilean satellites and more than an order of magnitude above Mercury's usual analogue, the Moon. The observations confirm that Mercury's anomalously high Na/K ratios cannot be explained by differences in neutral loss rates. The width and structure of the Na and K tails is comparable and both exhibit a persistent enhancement in their northern lobe. We interpret this as a signature of Mercury's offset magnetosphere; the exosphere's source rates are locally enhanced at the southern surface, and sloshing from radiation pressure and gravity guides this population into the northern region of the tail

The Rapid Imaging Planetary Spectrograph: Observations of Mercury's Sodium Exosphere in Twilight

International audienceGround-based observations of Mercury's exosphere are intrinsically difficult due to its proximity to the Sun and must be made in daylight or during brief windows at twilight. While the dimmer twilight background is far preferred, high airmass seeing and haze through Earth's atmosphere, windshake, and guiding all present formidable challenges toward spatially resolving the exosphere's structure. This study explores how such effects can be mitigated using results from a new instrument for high cadence spectroscopy, the Rapid Imaging Planetary Spectrograph. While high cadence observations do not significantly improve upon the resolution floor imposed by atmospheric seeing, the method does mitigate obstacles such as telescope tracking inaccuracy, windshake, and flux calibration. Whereas daytime observing has been the predominant methodology in past exosphere studies, the twilight observations performed here easily resolve distinct brightness enhancements near 50°-60°latitude, just equatorward of magnetic cusp regions. The exosphere in these locations is diagnostic of space weather effects such as charged particle precipitation. The structure in the sodium exosphere generally appears both more extended and brighter over the southern cusp, which has a broader open magnetic field line region. However, a northern enhancement during one observation confirms that the exosphere responds dynamically to environmental drivers, presumably changes in the solar wind dynamic pressure and/or interplanetary magnetic field