Michael J. Mumma

Strong Release of Methane on Mars in Northern Summer 2003

Living systems produce more than 90% of Earths atmospheric methane; the balance is of geochemical origin. On Mars, methane could be a signature of either origin. Using high-dispersion infrared spectrometers at three ground-based telescopes, we measured methane and water vapor simultaneously on Mars over several longitude intervals in northern early and late summer in 2003 and near the vernal equinox in 2006. When present, methane occurred in extended plumes, and the maxima of latitudinal profiles imply that the methane was released from discrete regions. In northern midsummer, the principal plume contained ∼19,000 metric tons of methane, and the estimated source strength (≥0.6 kilogram per second) was comparable to that of the massive hydrocarbon seep at Coal Oil Point in Santa Barbara, California.

Discovery of X-ray and Extreme Ultraviolet Emission from Comet C/Hyakutake 1996 B2

During its close approach to Earth, comet C/Hyakutake 1996 B2 was observed at extreme ultraviolet and x-ray wavelengths with the Rœntgen X-ray Satellite and Rossi X-ray Timing Explorer. The emission morphology was symmetric with respect to a vector from the comets nucleus toward the sun, but not symmetric around the direction of motion of the comet with respect to interplanetary dust. A slowly varying emission and a large impulsive event that varied on time scales of 1 to 2 hours were observed. An interaction between the comet and the solar wind/solar magnetic field seems to be the most likely mechanism for the observed emission.

Detection of Abundant Ethane and Methane, Along with Carbon Monoxide and Water, in Comet C/1996 B2 Hyakutake: Evidence for Interstellar Origin

The saturated hydrocarbons ethane (C2H6) and methane (CH4) along with carbon monoxide (CO) and water (H2O) were detected in comet C/1996 B2 Hyakutake with the use of high-resolution infrared spectroscopy at the NASA Infrared Telescope Facility on Mauna Kea, Hawaii. The inferred production rates of molecular gases from the icy, cometary nucleus (in molecules per second) are 6.4 × 1026 for C2H6, 1.2 × 1027 for CH4, 9.8 × 1027 for CO, and 1.7 × 1029 for H2O. An abundance of C2H6 comparable to that of CH4 implies that ices in C/1996 B2 Hyakutake did not originate in a thermochemically equilibrated region of the solar nebula. The abundances are consistent with a kinetically controlled production process, but production of C2H6 by gas-phase ion molecule reactions in the natal cloud core is energetically forbidden. The high C2H6/CH4 ratio is consistent with production of C2H6 in icy grain mantles in the natal cloud, either by photolysis of CH4-rich ice or by hydrogen-addition reactions to acetylene condensed from the gas phase.

Detection of water vapor in Halley's comet

Gaseous, neutral H2O was detected in the coma of comet Halley on 22.1 and 24.1 December 1985 Universal Time. Nine spectral lines of thev3 band (2.65 micrometers) were found by means of a Fourier transform spectrometer (λ/▵λ ∼ 105) on the NASA-Kuiper Airborne Observatory. The water production rate was ∼6 x 1028 molecules per second on 22.1 December and 1.7 x 1029 molecules per second on 24.1 December UT. The numbers of spectral lines and their intensities are in accord with nonthermal-equilibrium cometary models. Rotational populations are derived from the observed spectral line intensities and excitation conditions are discussed. The ortho-para ratio was found to be 2.66�0.13, corresponding to a nuclear-spin temperature of 32 K (+5 K, -2 K), possibly indicating that the observed water vapor originated from a low-temperature ice.

Remote infrared observations of parent volatiles in comets: A window on the early solar system

Abstract Organic volatiles and water in Oort Cloud comets were investigated at infrared wavelengths. The detected species include H 2 O, CO, CH 3 OH, CH 4 , C 2 H 2 , C 2 H 6 , OCS, HCN, NH 3 , and H 2 CO. Several daughter fragments (CN, OH, NH 2 , etc.) are also measured, and OH prompt emission provides a proxy for water. Long-slit spectra are taken at high spectral dispersion and high spatial resolution, eliminating several sources of systematic error. The resulting parent volatile production rates are highly robust, permitting a sensitive search for compositional diversity among comets. Here, seven OC comets are compared. Six (including Halley) exhibit similar compositions (excepting CO and CH 4 ). Their low formation temperatures (∼30 K) suggest this group probably formed beyond 30 AU from the young sun. However, C/1999 S4 is severely depleted in hypervolatiles and also in methanol, and it likely formed near 5–10 AU. C/2001 A2 is discussed briefly to illustrate future prospects.

A Survey of Organic Volatile Species in Comet C/1999 H1 (Lee) Using NIRSPEC at the Keck Observatory

The organic volatile composition of the long-period comet C/1999 H1 (Lee) was investigated using the —rst of a new generation of cross-dispersed cryogenic infrared spectrometers (NIRSPEC, at the Keck Observatory atop Mauna Kea, HI). On 1999 August 19¨21 the organics spectral region (2.9¨3.7 km) was completely sampled at both moderate and high dispersion, along with the CO fundamental region (near 4.67 km), revealing emission from water, carbon monoxide, methanol, methane, ethane, acetylene, and hydrogen cyanide. Many new multiplets from OH in the 1¨0 band were seen in prompt emission, and numerous new spectral lines were detected. Several spectral extracts are shown, and global production rates are presented for seven parent volatiles. Carbon monoxide is strongly depleted in comet Lee relative to comets Hyakutake and Hale-Bopp, demonstrating that chemical diversity occurred in the giant

Water Production Rates, Rotational Temperatures, and Spin Temperatures in Comets C/1999 H1 (Lee), C/1999 S4, and C/2001 A2

Water hot-band lines were detected in comets C/1999 H1 (Lee), C/1999 S4 (LINEAR), and C/2001 A2 (LINEAR) in the 2.9 � m spectral region using high-dispersion (k=� k � 2 ; 10 4 ) infrared spectroscopy with NIRSPEC at the W. M. Keck Observatory. The density of H2O emissions in this spectral region, the spectral coverage and resolution of NIRSPEC, and fluorescence models developed for these hot bands enabled the determination of H2O production rates, rotational temperatures, and ortho-to-para ratios (OPRs) in these comets. Previous studies revealed clear diversity in the volatile organic chemistries of these comets, suggesting that they may have formed in different regions of the early solar nebula. The nuclear spin temperature of H2O as derived from its OPR is another possible indicator of cometary formation temperature and region. Nuclear spin temperatures for H2O were derived on one date in comet S4 and two dates in Lee and A2. Derived spin temperatures for H2O in these comets are � 30, 30 þ15 � 6 ,a nd 23 þ4 � 3 K for S4, Lee, and A2, respectively. Measurements are consistent with a possible link between nuclear spin temperatures and volatile abundances, but studies of more comets and continued improvements in water hot-band fluorescence models are needed to more stringently test this. Subject headingg comets: general — comets: individual (C/1999 S4, C/2001 A2, Lee (C/1999 H1)) — infrared: solar system — techniques: spectroscopic

Identification of two sources of carbon monoxide in comet Hale-Bopp

The composition of ices in comets may reflect that of the molecular cloud in which the Sun formed, or it may show evidence of chemical processing in the pre-planetary accretion disk around the proto-Sun. As carbon monoxide (CO) is ubiquitous in molecular clouds,, its abundance with respect to water could help to determine the degree to which pre-cometary material was processed, although variations in CO abundance may also be influenced by the distance from the Sun at which comets formed. Observations have not hitherto provided an unambiguous measure of CO in the cometary ice (native CO). Evidence for an extended source of CO associated with comet Halley was provided by the Giotto spacecraft, but alternative interpretations exist. Here we report observations of comet Hale–Bopp which show that about half of the CO in the comet comes directly from ice stored in the nucleus. The abundance of this CO with respect to water (12 per cent) is smaller than in quiescent regions of molecular clouds, but is consistent with that measured in proto-stellar envelopes, suggesting that the ices underwent some processing before their inclusion into Hale–Bopp. The remaining CO arises in the coma, probably through thermal destruction of more complex molecules.

Comet outbursts and polymers of HCN

Dramatic cometary outbursts have been noted by observers for many years. These outbursts can sometimes increase the apparent brightness of a comet up to 9 mag and release energy on the order of 10 exp 19 ergs. A number of mechanisms have been suggested for outburst activity; however, none has been generally accepted. HCN is a known constituent of both interstellar icy grain mantles and cometary nuclei, and HCN polymers have been postulated to exist on the dark surface of comets such as P/Halley. Since polymerization is a strongly exothermic process, we investigate the possibility that HCN polymerization can provide the energy needed for outbursts. Polymerization may be continuing in the inhomogeneous interior of comets. In addition, the reactive CN groups in these oligomers can be hydrolyzed and may contribute to CO2 and CO pressure buildup in the interior of comets.

A SENSITIVE SEARCH FOR DEUTERATED WATER IN COMET 8P/TUTTLE*

We report a sensitive search for deuterated water (HDO) in comet 8P/Tuttle using high-resolution spectroscopy at infrared (IR) wavelengths. The deuterium enrichment of cometary water is one of the most important cosmogonic indicators in comets. The ratio preserves information about the conditions under which comet material formed, and tests the possible contribution of comets in delivering water for Earths oceans. Water (H2O) and HDO were sampled in comet 8P/Tuttle from 2008 January 27 to 2008 February 3 using the new IR spectrometer (Cryogenic Infrared Echelle Spectrograph) at the 8.2 m Antu telescope of the Very Large Telescope Observatory atop Cerro Paranal, Chile. Twenty-three lines of HDO were sampled near 3.7 μm, leading to a production rate of 4.73 ± 1.68 × 1025 s–1. Combining this value with the H2O production rate of 5790 ± 250 × 1025 s–1 provides a formal value of = 4.09 ± 1.45 × 10–4 in comet 8P/Tuttle. This value is larger by a factor of 2.62 ± 0.93 than Vienna Standard Mean Ocean Water, and is comparable to enrichment factors measured for three other Oort cloud comets. The technique described here provides unprecedented sensitivities, ultimately permitting us to routinely measure this prime cosmogonic indicator, even in comets having relatively modest gas production rate like 8P/Tuttle.