Tony L Farnham

Tony L Farnham
University of Maryland, College Park | UMD, UMCP, University of Maryland College Park · Department of Astronomy

BSAE, MSAE, MS Astronomy, PhD Astronomy

About

335
Publications
16,862
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7,823
Citations
Citations since 2017
28 Research Items
3795 Citations
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20172018201920202021202220230200400600800
20172018201920202021202220230200400600800

Publications

Publications (335)
Article
Full-text available
On 2022 September 26, the DART spacecraft will impact the surface of Dimorphos, the ∼160 m size satellite of the binary near-Earth asteroid (NEA) (65803) Didymos. What will be observed on the surfaces of both asteroids and at the DART impact site is largely unknown, beyond the details of Didymos revealed by previous Arecibo and Goldstone radar obse...
Article
Full-text available
We performed photometric observations of the binary near-Earth asteroid (65803) Didymos in support of the Double Asteroid Redirection Test (DART) mission that will test the Kinetic Impactor technology for diverting dangerous asteroids. It will hit the Didymos secondary, called Dimorphos, on 2022 September 26. We observed Didymos with 11 telescopes...
Preprint
Full-text available
We present a study of the current state of knowledge concerning spacecraft operations and potential hazards while operating near a comet nucleus. Starting from simple calculations comparing the cometary coma environment to benign conditions on Earth, we progress to sophisticated engineering models of spacecraft behavior, and then confront these mod...
Conference Paper
NASA’s Lucy mission is the first to provide flyby reconnaissance of the Jovian trojan asteroids, which are thought to be primordial small bodies that formed at a variety of heliocentric distances during the early stages of the solar system’s formation and were subsequently captured into Jupiter’s L4 and L5 Lagrange stability zones. Since its succes...
Article
Full-text available
We used long duration observations from the Transient Exoplanet Survey Satellite (TESS) to investigate the behavior of comet C/2014 UN271 Bernardinelli–Bernstein at large heliocentric distances. By combining data from sector 03 (976 30 minute exposures from 2018), and sectors 29 and 30 (3585 and 3410 10 minute exposures, respectively, from 2020), w...
Article
We present a study of the current state of knowledge concerning spacecraft operations and potential hazards while operating near a comet nucleus. Starting from some simple back of the envelope calculations comparing the cometary coma environment to benign conditions on Earth, we progress to sophisticated engineering models of spacecraft behavior, a...
Article
Long-period comet C/2021 A1 (Leonard) will approach Venus to within 0.029 au on 2021 December 18 and may subsequently graze the planet with its dust trail less than 2 days later. We observed C/2021 A1 with the Lowell Discovery Telescope on 2021 January 13 and March 3, as well as with the Palomar Hale Telescope on 2021 March 20, while the comet was...
Preprint
Long period comet C/2021 A1 (Leonard) will approach Venus to within 0.029 au on 2021 December 18 and may subsequently graze the planet with its dust trail less than two days later. We observed C/2021 A1 with the Lowell Discovery Telescope on 2021 January 13 and March 3, as well as with the Palomar Hale Telescope on 2021 March 20, while the comet wa...
Article
Full-text available
Cometary activity is a manifestation of sublimation-driven processes at the surface of nuclei. However, cometary outbursts may arise from other processes that are not necessarily driven by volatiles. In order to fully understand nuclear surfaces and their evolution, we must identify the causes of cometary outbursts. In that context, we present a st...
Article
Full-text available
We report on our extensive photometry and imaging of comet 46P/Wirtanen during its 2018/19 apparition and use these data to constrain the modeling of Wirtanen’s activity. Narrowband photometry was obtained in 9 epochs from 2018 October through 2019 March as well as 10 epochs during the 1991, 1997, and 2008 apparitions. The ensemble photometry revea...
Preprint
Full-text available
Cometary activity is a manifestation of sublimation-driven processes at the surface of nuclei. However, cometary outbursts may arise from other processes that are not necessarily driven by volatiles. In order to fully understand nuclear surfaces and their evolution, we must identify the causes of cometary outbursts. In that context, we present a st...
Preprint
We report on our extensive photometry and imaging of Comet 46P/Wirtanen during its 2018/19 apparition and use these data to constrain modeling of Wirtanen's activity. Narrowband photometry was obtained on nine epochs from 2018 October through 2019 March as well as 10 epochs during the 1991, 1997, and 2008 apparitions. The ensemble photometry reveal...
Article
Full-text available
We obtained broad- and narrowband images of the hyperactive comet 46P/Wirtanen on 33 nights during its 2018/2019 apparition, when the comet made a historic close approach to the Earth. With our extensive coverage, we investigated the temporal behavior of the comet on both seasonal and rotational timescales. We used CN observations to explore the co...
Preprint
We obtained broadband and narrowband images of the hyperactive comet 46P/Wirtanen on 33~nights during its 2018/2019 apparition, when the comet made an historic close approach to the Earth. With our extensive coverage, we investigated the temporal behavior of the comet on both seasonal and rotational timescales. CN observations were used to explore...
Preprint
We report the recovery of returning Halley-type comet 12P/Pons-Brooks using the 4.3 m Lowell Discovery Telescope, at a heliocentric distance of 11.89 au. Comparative analysis with a dust model suggests that the comet may have been active since $\sim30$ au from the Sun. We derive a nucleus radius of $17\pm6$ km from the nucleus photometry, though th...
Preprint
We report on initial results from 20 days' worth of TESS spacecraft observations of comet 46P/Wirtanen. The long-duration, high-cadence measurements show a 2018 September 26 outburst that exhibited a two-phase, 0.5 mag brightening profile, and may be the best temporally characterized natural outburst ever recorded. Gas velocities from the outburst...
Article
Comets are primitive objects that formed in the protoplanetary disk, and have been largely preserved over the history of the solar system. However, they are not pristine, and surfaces of cometary nuclei do evolve. In order to understand the extent of their primitive nature, we must define the mechanisms that affect their surfaces and comae. We exam...
Preprint
Comets are primitive objects that formed in the protoplanetary disk, and have been largely preserved over the history of the Solar System. However, they are not pristine, and surfaces of cometary nuclei do evolve. In order to understand the extent of their primitive nature, we must define the mechanisms that affect their surfaces and comae. We exam...
Article
Full-text available
The Zwicky Transient Facility (ZTF), a public–private enterprise, is a new time-domain survey employing a dedicated camera on the Palomar 48-inch Schmidt telescope with a 47 deg ² field of view and an 8 second readout time. It is well positioned in the development of time-domain astronomy, offering operations at 10% of the scale and style of the La...
Article
Full-text available
The Zwicky Transient Facility (ZTF) is a new optical time-domain survey that uses the Palomar 48 inch Schmidt telescope. A custom-built wide-field camera provides a 47 deg^2 field of view and 8 s readout time, yielding more than an order of magnitude improvement in survey speed relative to its predecessor survey, the Palomar Transient Factory. We d...
Preprint
Full-text available
The Zwicky Transient Facility (ZTF), a public-private enterprise, is a new time domain survey employing a dedicated camera on the Palomar 48-inch Schmidt telescope with a 47 deg$^2$ field of view and 8 second readout time. It is well positioned in the development of time domain astronomy, offering operations at 10% of the scale and style of the Lar...
Article
Full-text available
Cometary outgassing can produce torques that change the spin state of the nucleus, influencing the evolution and lifetimes of comets (1,2). If these torques spin up the rotation to the point that centripetal forces exceed the material strength of the nucleus, the comet may fragment (3). Torques that slow down the rotation can cause the spin state t...
Article
We observed the newly discovered hyperbolic minor planet A/2017 U1 on 2017 October 30 with the 4.3-m Discovery Channel Telescope. From these observations, we derived a partial lightcurve with variability of at least 1.2 mag. This lightcurve segment rules out rotation periods less than 3 hr and suggests the period is at least 5 hr. On the assumption...
Article
Full-text available
We present a community-led assessment of the capabilities of NASA's Wide Field InfraRed Survey Telescope (WFIRST) for Solar System science. WFIRST will provide imaging and spectroscopic capabilities from 0.6-2.0 $\mu$m and will be a potential contemporary and eventual successor to JWST. Observations of asteroids, the giant planets and their satelli...
Article
The Deep Impact spacecraft observed comet C/2012 S1 (ISON) between 17 January and 10 March 2013 when the comet was ∼5 AU from the Sun. Continuous, high-cadence, images spanning as much as 6 days at a time, and high-cadence IR spectral scans spanning 2 days, represent the most intensive set of observations available from the early part of ISON's app...
Article
Spacecraft missions have resolved the nuclei of six periodic comets and revealed a set of geologically intriguing and active small bodies. The shapes of these cometary nuclei are dominantly bilobate reflecting their formation from smaller cometesimals. Cometary surfaces include a diverse set of morphologies formed from a variety of mechanisms. Subl...
Article
We observed Comet C/Siding Spring using the Hubble Space Telescope (HST) during its close approach to Mars. The high spatial resolution images obtained through the F689M, F775W, and F845M filters reveal the characteristics of the dust coma. The dust production rate of C/Siding Spring, quantified by $Af\rho$, is 590$\pm$30, 640$\pm$30, and 670$\pm$3...
Article
Full-text available
The James Webb Space Telescope (JWST), as the largest space-based astronomical observatory with near- and mid-infrared instrumentation, will elucidate many mysterious aspects of comets. We summarize four cometary science themes especially suited for this telescope and its instrumentation: the drivers of cometary activity, comet nucleus heterogeneit...
Article
Full-text available
We present the results of a global coma morphology campaign for comet C/2012 S1 (ISON), which was organized to involve both professional and amateur observers. In response to the campaign, many hundreds of images, from nearly two dozen groups were collected. Images were taken primarily in the continuum, which help to characterize the behavior of du...
Article
We used the UltraViolet-Optical Telescope on board Swift to systematically follow the dynamically new comet C/2013 A1 (Siding Spring) on its approach to the Sun. The comet was observed from a heliocentric distance of 4.5 AU pre-perihelion to its perihelion at 1.4 AU. From our observations, we estimate that the water production rate during closest a...
Article
Full-text available
The close encounter of Comet C/2013 A1 (Siding Spring) with Mars on October 19, 2014 presented an extremely rare opportunity to obtain the first flyby quality data of the nucleus and inner coma of a dynamically new comet. However, the comet's dust tail potentially posed an impact hazard to those spacecraft. To characterize the comet at large helioc...
Article
We analyzed Deep Impact High Resolution Instrument (HRI) images acquired within the first seconds after collision of the Deep Impact impactor with the nucleus of comet 9 P/Tempel 1. These images reveal an optically thick ejecta plume that casts a shadow on the surface of the nucleus. Using the 3D radiative transfer code HYPERION we simulated light...
Article
Although the nucleus of comet C/2013 A1 (Siding Spring) will safely pass Mars in October 2014, the dust in the coma and tail will more closely approach the planet. Using a dynamical model of comet dust, we estimate the impact fluence. Based on our nominal model no impacts are expected at Mars. Relaxing our nominal model's parameters, the fluence is...
Article
On November 4th, 2010, the Deep Impact eXtended Investigation (DIXI) successfully encountered comet 103P/Hartley 2, when it was at a heliocentric distance of 1.06 AU. Spatially resolved near-IR spectra of comet Hartley 2 were acquired in the 1.05–4.83 μm wavelength range using the HRI-IR spectrometer. We present spectral maps of the inner ∼∼10 km o...
Article
Full-text available
Comet C/2013 A1 (Siding Spring) will have a close encounter with Mars on October 19, 2014. We model the dynamical evolution of dust grains from the time of their ejection from the comet nucleus to the Mars close encounter, and determine the flux at Mars. Constraints on the ejection velocity from Hubble Space Telescope observations indicate that the...
Article
Comet C/2013 A1 (siding Spring) will experience a high velocity encounter with Mars on October 19, 2014 at a distance of 135,000 km +- 5000 km from the planet center. We present a comprehensive analysis of the trajectory of both the comet nucleus and the dust tail. The nucleus of C/2013 A1 cannot impact on Mars even in the case of unexpectedly larg...
Article
Comet C/2013 A1 (siding Spring) will experience a high velocity encounter with Mars on October 19, 2014 at a distance of 135,000 km +- 5000 km from the planet center. We present a comprehensive analysis of the trajectory of both the comet nucleus and the dust tail. The nucleus of C/2013 A1 cannot impact on Mars even in the case of unexpectedly larg...
Article
Comet C/2013 A1 (Siding Spring) will pass Mars at the extremely close distance of 136,000 km in Oct 2014, giving Mars orbiting spacecraft an up-close and unprecedented view of this dynamically new comet. However, 100 minutes after the closest approach to the nucleus, Mars passes within 30,000 km of the comet's orbit. Here, large dust grains may be...
Article
The High Resolution Instrument Infrared Spectrometer (HRI-IR) onboard the Deep Impact Flyby spacecraft detected H2O, CO2, and CO in the coma of the dynamically young Oort cloud comet C/2009 P1 (Garradd) post-perihelion at a heliocentric distance of 2 AU. Production rates were derived for the parent volatiles, QH2O = 4.6e28, QCO2 = 3.9e27, and QCO =...
Article
Full-text available
We report results from broadband visible images of comet C/2012 S1 (ISON) obtained with the Hubble Space Telescope Wide Field Camera 3 on 2013 April 10. C/ISON's coma brightness follows a 1/{\rho} (where {\rho} is the projected distance from the nucleus) profile out to 5000 km, consistent with a constant speed dust outflow model. The turnaround dis...
Article
The Deep Impact flyby spacecraft (DI) is currently operating as a remote observatory, studying bright comets from a different perspective than can be achieved from Earth. Images are obtained with the Medium Resolution Imager (MRI) using a broadband CLEAR filter to capture the continuum, and narrowband filters to capture OH, CN and C2 gas bands (Far...
Article
We have assembled a variety of data on the early behavior of comet ISON through early June 2013, including V magnitudes from the ground and from spacecraft (SWIFT, DIFlyby), upper limits on gas from the DIFlyby, Herschel, and Hubble, and ground-based detections of CO and CN. We argue that the comet’s activity was steadily increasing from the pre-di...
Article
NASA’s EPOXI mission used the Deep Impact (DI) Flyby spacecraft to deliver a payload of three scientific instruments, two visible cameras and an IR spectrometer, to a close flyby of Comet 103P/Hartley 2 in November 2010. Interpretation of the scientific measurements made using these instruments depends on accurate calibration of the instruments’ pe...
Article
Re-calibrated near-infrared spectroscopy of the resolved nucleus of Comet 9P/Tempel 1 acquired by the Deep Impact spacecraft has been analyzed by utilizing the post-Stardust-NExT nucleus shape model and spin pole solution, as well as a novel thermophysical model that explicitly accounts for small-scale surface roughness and thermal inertia. We find...
Article
CBET 3496 available at Central Bureau for Astronomical Telegrams.
Article
NASA’s Stardust–NExT mission used the Stardust spacecraft to deliver a scientific payload, including a panchromatic visible camera designated NAVCAM, to a close flyby of Comet 9P/Tempel 1 in February 2011. Proper interpretation of the NAVCAM images depends on accurate calibration of the camera performance. While the NAVCAM had been calibrated durin...
Article
The Deep Impact Spacecraft flew past Comet 103P/Hartley 2 on November 4th, 2010. Images revealed the comet to be enveloped in a field of debris composed of fine grained dust, ice, and hundreds of discrete millimeter to decimeter sized particles. In this work, a selection of the brightest particles are identified and photogrammetrically located in 3...
Article
The analysis of continuum images of Comet 103P/Hartley 2 taken at the Kitt Peak National Observatory in 2010 is presented. Two distinct near-radial sunward continuum features were observed in the comet in November, while one sunward continuum feature is identified in images from October and December, 2010. The morphology and spatial extent of the c...
Article
The EPOXI mission flyby of Comet 103P/Hartley 2 revealed numerous discrete dust jets extending from the nucleus, thereby providing an unprecedented opportunity to visually connect these features to the nuclear surface. The observed distribution of jets yields fresh insight into the conditions under which these cometary features may form. This study...
Article
Full-text available
We describe recent results on the CO/CO{sub 2}/H{sub 2}O composition of comets together with a survey of older literature (primarily for CO/H{sub 2}O) and compare these with models of the protoplanetary disk. Even with the currently small sample, there is a wide dispersion in abundance ratios and little if any systematic difference between Jupiter-...
Article
Full-text available
We report on photometry and imaging of Comet 10P/Tempel 2 obtained at Lowell Observatory from 1983 through 2011. We measured a nucleus rotation period of 8.950 +/- 0.002 hr from 2010 September to 2011 January. This rotation period is longer than the period we previously measured in 1999, which was itself longer than the period measured in 1988. A n...
Conference Paper
The target of the NASA DIXI mission, comet 103P/Hartley 2 is in a non-principal-axis (NPA) rotational state that was observed to be varying with time. However, there is still no consensus on the specific NPA rotational state during the 103P/Hartley 2 encounter by DIXI. We analyze the continuum features observed in ground-based images bracketing the...
Article
In 2012, the Deep Impact (DI) spacecraft observed comet C/2009 P1 Garradd during its post-perihelion passage through the inner Solar System. The HRI-IR observations of Garradd (1.05-4.85 microns) were made on March 26 and April 2 when Garradd was at a heliocentric distance of 2 AU. All three dominant cometary volatiles, H2O, CO2, and CO, were detec...
Conference Paper
We report on our multi-epoch observations of Comet 10P/Tempel 2, primarily from Lowell Observatory. We obtained narrowband photometry during the 1983, 1988, 1999, and 2010 apparitions. Tempel 2 exhibited a rapid “turn-on” in activity 90 days prior to perihelion, with the date of turn on varying somewhat from apparition to apparition. Peak productio...
Article
The Deep Impact eXtended Investigation (DIXI) to comet 103P/Hartley 2 culminated in a closest approach (CA) of 700 km on November 4th, 2010, when the comet was at 1.064 astronomical units (AU) from the Sun. In visible images at closest approach, comet Hartley 2 displays jets off the end of the smaller lobe of the nucleus and beyond the terminator a...
Article
The Deep Impact spacecraft observed comet C/2009 P1 Garradd with the Medium Resolution Instrument at ∼hourly intervals from 2012 Feb 20 to Mar 7, with additional observations between Mar 25 and Apr 8. Images were obtained with the broadband CLEAR filter and narrowband CN, OH, C2 and Green Continuum filters. During the time of the observations, the...
Article
We report on space-borne observations of comet C/2009 P1 (Garradd) using Swift’s UV-Optical Telescope (UVOT). C/2009 P1 is a dynamically new comet and this is likely its first journey to the inner solar system since its emplacement in the Oort cloud. It was discovered in 2009 and clearly exhibited a dust coma as far as 8.5 AU from the Sun. We obser...
Conference Paper
Full-text available
We report on our multiepoch observations (photometry and imaging) of Comet 10P/Tempel 2, primarily from Lowell Observatory. We find strong seasonal effects, a "typical" composition, and a change in the rotation period between 1999 and 2010.
Article
Comet 103P/Hartley 2 had a very close approach to Earth and was successfully encountered by the EPOXI mission in 2010. We observed the comet with the Kitt Peak 2.1m telescope September 1-3, September 30 - October 4, November 2-8, and December 11-15 with broadband R and narrowband HB comet filters. Results on the structures seen in the CN coma were...
Article
Previous comet flyby missions enabled detailed studies of the photometric properties of several cometary nuclei from disk-resolved images, including 9P/Tempel 1, 19P/Borrelly, and 81P/Wild 2. Two recent missions, DIXI and Stardust-NExT, encountered Comets 103P/Hartley 2 and Tempel 1 respectively, expanding the pool of sampled cometary nuclei in the...
Article
The NASA Planetary Data System contains a large range of asteroid, comet, and other small bodies data obtained from spacecraft and ground-based facilities. The Small Bodies Data Ferret is a tool for searching and accessing this data.
Article
We present and analysis of the excited spin state of comet 103P/Hartley and show how the total angular momentum varies through the DIXI encounter.
Article
CBET 3090 available at Central Bureau for Astronomical Telegrams.