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Ballantyne HA, Asphaug E, Denton CA, Emsenhuber A, Jutzi M. Sputnik Planitia as an impactor remnant indicative of an ancient rocky mascon in an oceanless Pluto. NATURE ASTRONOMY 2024; 8:748-755. [PMID: 38912293 PMCID: PMC11189809 DOI: 10.1038/s41550-024-02248-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 01/17/2023] [Accepted: 03/12/2024] [Indexed: 06/25/2024]
Abstract
Pluto's surface is dominated by the huge, pear-shaped basin Sputnik Planitia. It appears to be of impact origin, but modelling has not yet explained its peculiar geometry. We propose an impact mechanism that reproduces its topographic shape while also explaining its alignment near the Pluto-Charon axis. Using three-dimensional hydrodynamic simulations to model realistic collisions, we provide a hypothesis that does not rely upon a cold, stiff crust atop a contrarily liquid ocean where a differentiated ~730 km ice-rock impactor collides at low-velocity into a subsolidus Pluto-like target. The result is a new geologic region dominated by impactor material, namely a basin that (in a 30° collision) closely reproduces the morphology of Sputnik Planitia, and a captured rocky impactor core that has penetrated the ice to accrete as a substantial, strength-supported mascon. This provides an alternative explanation for Sputnik Planitia's equatorial alignment and illustrates a regime in which strength effects, in low-velocity collisions between trans-Neptunian objects, lead to impactor-dominated regions on the surface and at depth.
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Affiliation(s)
- Harry A. Ballantyne
- Space Research and Planetary Sciences, Physics Institute, University of Bern, Bern, Switzerland
| | - Erik Asphaug
- Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ USA
| | - C. Adeene Denton
- Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ USA
| | - Alexandre Emsenhuber
- Space Research and Planetary Sciences, Physics Institute, University of Bern, Bern, Switzerland
- University Observatory, Ludwig-Maximilians Universität München, Munich, Germany
| | - Martin Jutzi
- Space Research and Planetary Sciences, Physics Institute, University of Bern, Bern, Switzerland
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2
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Emran A, Dalle Ore CM, Ahrens CJ, Khan MKH, Chevrier VF, Cruikshank DP. Pluto’s Surface Mapping Using Unsupervised Learning from Near-infrared Observations of LEISA/Ralph. THE PLANETARY SCIENCE JOURNAL 2023; 4:15. [DOI: 10.3847/psj/acb0cc] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 09/01/2023]
Abstract
Abstract
We map the surface of Pluto using an unsupervised machine-learning technique using the near-infrared observations of the LEISA/Ralph instrument on board NASA’s New Horizons spacecraft. The principal-component-reduced Gaussian mixture model was implemented to investigate the geographic distribution of the surface units across the dwarf planet. We also present the likelihood of each surface unit at the image pixel level. Average I/F spectra of each unit were analyzed—in terms of the position and strengths of absorption bands of abundant volatiles such as N2, CH4, and CO and nonvolatile H2O—to connect the unit to surface composition, geology, and geographic location. The distribution of surface units shows a latitudinal pattern with distinct surface compositions of volatiles—consistent with the existing literature. However, previous mapping efforts were based primarily on compositional analysis using spectral indices (indicators) or implementation of complex radiative transfer models, which need (prior) expert knowledge, label data, or optical constants of representative end-members. We prove that an application of unsupervised learning in this instance renders a satisfactory result in mapping the spatial distribution of ice compositions without any prior information or label data. Thus, such an application is specifically advantageous for a planetary surface mapping when label data are poorly constrained or completely unknown, because an understanding of surface material distribution is vital for volatile transport modeling at the planetary scale. We emphasize that the unsupervised learning used in this study has wide applicability and can be expanded to other planetary bodies of the solar system for mapping surface material distribution.
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3
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Endogenically sourced volatiles on Charon and other Kuiper belt objects. Nat Commun 2022; 13:4457. [PMID: 35945207 PMCID: PMC9363412 DOI: 10.1038/s41467-022-31846-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2021] [Accepted: 07/01/2022] [Indexed: 11/18/2022] Open
Abstract
Kuiper belt objects (KBOs) have diverse surface compositions, and the New Horizons mission to the Pluto-Charon system allows us to test hypotheses on the origin and evolution of these KBO surfaces. Previous work proposed that Charon’s organic-rich north pole formed from radiolytically processed volatiles sourced from Pluto’s escaping atmosphere. Here, we show an endogenic source of volatiles from Charon’s interior is plausible. We calculate that cryovolcanic resurfacing released 1.29 × 1015–3.47 × 1015 kg of methane to Charon’s surface from its interior. We modeled volatile transport and found the vast majority of this volcanically released methane migrates to Charon’s poles, with deposition rates sufficient to be processed into the observed organic compounds. Irradiated methane products appear on similarly sized KBOs that do not orbit a Pluto-sized object to draw an escaping atmosphere from, so interior-sourced volatiles could be a common and important process across the Kuiper belt. We show cryovolcanic eruptions released sufficient methane to source volatile products on Charon. Irradiated methane products are found on other Kuiper belt objects, so endogenically sourced volatiles could be important across the Kuiper belt.
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Morison A, Labrosse S, Choblet G. Sublimation-driven convection in Sputnik Planitia on Pluto. Nature 2021; 600:419-423. [PMID: 34912087 DOI: 10.1038/s41586-021-04095-w] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2021] [Accepted: 10/04/2021] [Indexed: 11/09/2022]
Abstract
Sputnik Planitia is a nitrogen-ice-filled basin on Pluto1. Its polygonal surface patterns2 have been previously explained as a result of solid-state convection with either an imposed heat flow3 or a temperature difference within the 10-km-thick ice layer4. Neither explanation is satisfactory, because they do not exhibit surface topography with the observed pattern: flat polygons delimited by narrow troughs5. Internal heating produces the observed patterns6, but the heating source in such a setup remains enigmatic. Here we report the results of modelling the effects of sublimation at the surface. We find that sublimation-driven convection readily produces the observed polygonal structures if we assume a smaller heat flux (~0.3 mW m-2) at the base of the ice layer than the commonly accepted value of 2-3 mW m-2 (ref. 7). Sustaining this regime with the latter value is also possible, but would require a stronger viscosity contrast (~3,000) than the nominal value (~100) considered in this study.
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Affiliation(s)
| | | | - Gaël Choblet
- Laboratoire de Planétologie et Géodynamique, UMR 6112, Nantes Université, CNRS, Université d'Angers, Nantes, France
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Cruikshank DP, Materese CK, Pendleton YJ, Boston PJ, Grundy WM, Schmitt B, Lisse CM, Runyon KD, Keane JT, Beyer RA, Summers ME, Scipioni F, Stern SA, Dalle Ore CM, Olkin CB, Young LA, Ennico K, Weaver HA, Bray VJ. Prebiotic Chemistry of Pluto. ASTROBIOLOGY 2019; 19:831-848. [PMID: 30907634 DOI: 10.1089/ast.2018.1927] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
We present the case for the presence of complex organic molecules, such as amino acids and nucleobases, formed by abiotic processes on the surface and in near-subsurface regions of Pluto. Pluto's surface is tinted with a range of non-ice substances with colors ranging from light yellow to red to dark brown; the colors match those of laboratory organic residues called tholins. Tholins are broadly characterized as complex, macromolecular organic solids consisting of a network of aromatic structures connected by aliphatic bridging units (e.g., Imanaka et al., 2004; Materese et al., 2014, 2015). The synthesis of tholins in planetary atmospheres and in surface ices has been explored in numerous laboratory experiments, and both gas- and solid-phase varieties are found on Pluto. A third variety of tholins, exposed at a site of tectonic surface fracturing called Virgil Fossae, appears to have come from a reservoir in the subsurface. Eruptions of tholin-laden liquid H2O from a subsurface aqueous repository appear to have covered portions of Virgil Fossae and its surroundings with a uniquely colored deposit (D.P. Cruikshank, personal communication) that is geographically correlated with an exposure of H2O ice that includes spectroscopically detected NH3 (C.M. Dalle Ore, personal communication). The subsurface organic material could have been derived from presolar or solar nebula processes, or might have formed in situ. Photolysis and radiolysis of a mixture of ices relevant to Pluto's surface composition (N2, CH4, CO) have produced strongly colored, complex organics with a significant aromatic content having a high degree of nitrogen substitution similar to the aromatic heterocycles pyrimidine and purine (Materese et al., 2014, 2015; Cruikshank et al., 2016). Experiments with pyrimidines and purines frozen in H2O-NH3 ice resulted in the formation of numerous nucleobases, including the biologically relevant guanine, cytosine, adenine, uracil, and thymine (Materese et al., 2017). The red material associated with the H2O ice may contain nucleobases resulting from energetic processing on Pluto's surface or in the interior. Some other Kuiper Belt objects also exhibit red colors similar to those found on Pluto and may therefore carry similar inventories of complex organic materials. The widespread and ubiquitous nature of similarly complex organic materials observed in a variety of astronomical settings drives the need for additional laboratory and modeling efforts to explain the origin and evolution of organic molecules. Pluto observations reveal complex organics on a small body that remains close to its place of origin in the outermost regions of the Solar System.
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Affiliation(s)
- D P Cruikshank
- 1NASA Ames Research Center, Moffett Field, California, USA
| | - C K Materese
- 2Goddard Space Flight Center, Greenbelt, Maryland, USA
| | - Y J Pendleton
- 1NASA Ames Research Center, Moffett Field, California, USA
| | - P J Boston
- 1NASA Ames Research Center, Moffett Field, California, USA
| | - W M Grundy
- 3Lowell Observatory, Flagstaff, Arizona, USA
| | - B Schmitt
- 4Université Grenoble Alpes, CNRS, IPAG, Grenoble, France
| | - C M Lisse
- 5Applied Physics Laboratory, Johns Hopkins University, Laurel, Maryland, USA
| | - K D Runyon
- 5Applied Physics Laboratory, Johns Hopkins University, Laurel, Maryland, USA
| | - J T Keane
- 6California Institute of Technology, Pasadena, California, USA
| | - R A Beyer
- 1NASA Ames Research Center, Moffett Field, California, USA
| | - M E Summers
- 7Department of Physics and Astronomy, George Mason University, Fairfax, Virginia, USA
| | - F Scipioni
- 1NASA Ames Research Center, Moffett Field, California, USA
| | - S A Stern
- 8Southwest Research Institute, Boulder, Colorado, USA
| | - C M Dalle Ore
- 1NASA Ames Research Center, Moffett Field, California, USA
| | - C B Olkin
- 8Southwest Research Institute, Boulder, Colorado, USA
| | - L A Young
- 8Southwest Research Institute, Boulder, Colorado, USA
| | - K Ennico
- 1NASA Ames Research Center, Moffett Field, California, USA
| | - H A Weaver
- 5Applied Physics Laboratory, Johns Hopkins University, Laurel, Maryland, USA
| | - V J Bray
- 9Lunar and Planetary Laboratory, University of Arizona, Tucson, Arizona, USA
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Dalle Ore CM, Cruikshank DP, Protopapa S, Scipioni F, McKinnon WB, Cook JC, Grundy WM, Schmitt B, Stern SA, Moore JM, Verbiscer A, Parker AH, Singer KN, Umurhan OM, Weaver HA, Olkin CB, Young LA, Ennico K. Detection of ammonia on Pluto's surface in a region of geologically recent tectonism. SCIENCE ADVANCES 2019; 5:eaav5731. [PMID: 31608308 PMCID: PMC6771079 DOI: 10.1126/sciadv.aav5731] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 09/28/2018] [Accepted: 04/25/2019] [Indexed: 06/10/2023]
Abstract
We report the detection of ammonia (NH3) on Pluto's surface in spectral images obtained with the New Horizons spacecraft that show absorption bands at 1.65 and 2.2 μm. The ammonia signature is spatially coincident with a region of past extensional tectonic activity (Virgil Fossae) where the presence of H2O ice is prominent. Ammonia in liquid water profoundly depresses the freezing point of the mixture. Ammoniated ices are believed to be geologically short lived when irradiated with ultraviolet photons or charged particles. Thus, the presence of NH3 on a planetary surface is indicative of a relatively recent deposition or possibly through exposure by some geological process. In the present case, the areal distribution is more suggestive of cryovolcanic emplacement, however, adding to the evidence for ongoing geological activity on Pluto and the possible presence of liquid water at depth today.
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Affiliation(s)
- C. M. Dalle Ore
- SETI Institute, Mountain View CA, USA
- NASA Ames Research Center, Moffett Field CA, USA
| | | | | | - F. Scipioni
- SETI Institute, Mountain View CA, USA
- NASA Ames Research Center, Moffett Field CA, USA
| | - W. B. McKinnon
- Department of Earth and Planetary Sciences and the McDonnell Center for the Space Sciences, Washington University, St. Louis, MO, USA
| | | | | | - B. Schmitt
- Université Grenoble Alpes, CNRS, IPAG, F-38000 Grenoble, France
| | - S. A. Stern
- Southwest Research Institute, Boulder CO, USA
| | - J. M. Moore
- NASA Ames Research Center, Moffett Field CA, USA
| | - A. Verbiscer
- Johns Hopkins University Applied Physics Laboratory, Laurel MD, USA
| | | | | | - O. M. Umurhan
- SETI Institute, Mountain View CA, USA
- NASA Ames Research Center, Moffett Field CA, USA
| | - H. A. Weaver
- University of Virginia, Charlottesville, VA, USA
| | - C. B. Olkin
- Southwest Research Institute, Boulder CO, USA
| | - L. A. Young
- Southwest Research Institute, Boulder CO, USA
| | - K. Ennico
- NASA Ames Research Center, Moffett Field CA, USA
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7
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Barr AC. Pluto's telltale heart. Nature 2016; 540:42-43. [DOI: 10.1038/540042a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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8
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Hamilton DP, Stern SA, Moore JM, Young LA. The rapid formation of Sputnik Planitia early in Pluto's history. Nature 2016; 540:97-99. [PMID: 27905411 DOI: 10.1038/nature20586] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2016] [Accepted: 10/28/2016] [Indexed: 11/09/2022]
Abstract
Pluto's Sputnik Planitia is a bright, roughly circular feature that resembles a polar ice cap. It is approximately 1,000 kilometres across and is centred on a latitude of 25 degrees north and a longitude of 175 degrees, almost directly opposite the side of Pluto that always faces Charon as a result of tidal locking. One explanation for its location includes the formation of a basin in a giant impact, with subsequent upwelling of a dense interior ocean. Once the basin was established, ice would naturally have accumulated there. Then, provided that the basin was a positive gravity anomaly (with or without the ocean), true polar wander could have moved the feature towards the Pluto-Charon tidal axis, on the far side of Pluto from Charon. Here we report modelling that shows that ice quickly accumulates on Pluto near latitudes of 30 degrees north and south, even in the absence of a basin, because, averaged over its orbital period, those are Pluto's coldest regions. Within a million years of Charon's formation, ice deposits on Pluto concentrate into a single cap centred near a latitude of 30 degrees, owing to the runaway albedo effect. This accumulation of ice causes a positive gravity signature that locks, as Pluto's rotation slows, to a longitude directly opposite Charon. Once locked, Charon raises a permanent tidal bulge on Pluto, which greatly enhances the gravity signature of the ice cap. Meanwhile, the weight of the ice in Sputnik Planitia causes the crust under it to slump, creating its own basin (as has happened on Earth in Greenland). Even if the feature is now a modest negative gravity anomaly, it remains locked in place because of the permanent tidal bulge raised by Charon. Any movement of the feature away from 30 degrees latitude is countered by the preferential recondensation of ices near the coldest extremities of the cap. Therefore, our modelling suggests that Sputnik Planitia formed shortly after Charon did and has been stable, albeit gradually losing volume, over the age of the Solar System.
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Affiliation(s)
| | | | - J M Moore
- NASA Ames, Mountain View, California, USA
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Nimmo F, Hamilton DP, McKinnon WB, Schenk PM, Binzel RP, Bierson CJ, Beyer RA, Moore JM, Stern SA, Weaver HA, Olkin CB, Young LA, Smith KE. Reorientation of Sputnik Planitia implies a subsurface ocean on Pluto. Nature 2016; 540:94-96. [DOI: 10.1038/nature20148] [Citation(s) in RCA: 85] [Impact Index Per Article: 10.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2016] [Accepted: 10/03/2016] [Indexed: 11/09/2022]
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