Fly Over Pluto

Video is based on data and images from New Horizons.

Makemake has a Surprisingly Uniform Surface

The very homogeneous surface of the dwarf planet Makemake

Authors:

Perna et al

Abstract:

The dwarf planet (136472) Makemake is one of the largest trans-Neptunian objects discovered to date. Noteworthy, the size and surface temperature of this celestial body put it in a transition region where nitrogen is preferentially lost, while the less volatile methane is retained. Indeed, literature spectra clearly show that the surface of Makemake is dominated by methane ice, though the presence of nitrogen and of irradiation products of methane has been inferred by several authors, and a debate is still open about the eventual rotational variability of the surface composition. In this work we present new visible and near-infrared spectra of Makemake obtained with the TNG telescope (La Palma, Spain) in the time span 2006–2013. Our data sample different rotational phases, covering about 80% of the surface. All of the obtained spectra look very similar, suggesting an overall homogeneous composition. No secular variations appear when comparing our data to literature results (as expected, considering the quite short orbital arc travelled by Makemake since its discovery in 2005). The presence of methane diluted in nitrogen is evidenced by the shift of the observed absorption bands with respect to those of pure methane, with a dilution state looking homogeneous over the surface. We modelled a complete visible and near-infrared spectrum of Makemake using the Shkuratov formalism, and found that adding irradiation products of methane like ethane and ethylene seems indeed improving the fit of the synthetic spectrum to our data. We found no hints of a localized/temporary atmosphere.

The Puzzling Detection of X-rays From Pluto by Chandra

The Puzzling Detection of X-rays From Pluto by Chandra

Authors:

Lisse et al

Abstract:

Using Chandra ACIS-S, we have obtained imaging Xray spectrophotometry of the Pluto system in support of the New Horizons flyby on 14 July 2015. 174 ksec of observations were obtained on 4 visits in Feb 2014 to Aug 2015. We measured a net signal of 6.8 counts and a noise level of 1.2 counts in a comoving 11 x 11 pixel box (100 x 100 R_Pluto) in the 0.31 to 0.60 keV passband for a detection at > 99.95 C.L. The Pluto photons do not match the background spectrum, are coincident with a 90% flux aperture comoving with Pluto, and are not sky source confused. The mean 0.31 to 0.60 keV Xray power from Pluto is 200 MW, in the midrange of Xray power levels seen for known solar system emission sources: auroral precipitation, solar Xray scattering, and charge exchange (CXE) between solar wind (SW) ions & atmospheric neutrals. We eliminate auroral effects as a source, as Pluto has no known magnetic field & the New Horizons Alice UV spectrometer detected no airglow from Pluto during the flyby. Nano-scale atmospheric haze particles could lead to enhanced resonant scattering of solar X-rays from Pluto, but the energy signature of the detected photons does not match the solar spectrum and estimates of Plutos scattered Xray emission are > 100 times below the 3.9e-5 cps found in our observations. CXE emission from SW carbon, nitrogen, and oxygen ions can produce the energy signature seen, and the 6e25 neutral gas escape rate from Pluto deduced from New Horizons data can support the 3.0e24 Xray photons/sec emission rate required by our observations. Using the SW proton density and speed measured by the Solar Wind Around Pluto (SWAP) instrument in the vicinity of Pluto at the time of the photon emissions, we find too few SW minor ions flowing into the 11 x 11 pixel box centered on Pluto than are needed to support the observed emission rate unless the SW is significantly focused and enhanced in this region.

Sputnik Planitia may Dominate Pluto

Icy heart could be key to Pluto’s strange geology

Author:

Witze

Abstract:

Pluto’s icy heart beats with a planetary rhythm.

When NASA’s New Horizons spacecraft whizzed by the dwarf planet in July 2015, it famously spotted a heart-shaped feature just north of the equator. Now, researchers are recognizing how that enormous ice cap drives much of Pluto’s activity, from its frosty surface to its hazy atmosphere.

Planetary scientists revealed their latest insights this week at a joint meeting of the American Astronomical Society’s Division for Planetary Sciences and the European Planetary Science Congress in Pasadena, California. Many of those discoveries revolve around Sputnik Planitia, the icy expanse that makes up the left lobe of Pluto’s ‘heart’. “All roads lead to Sputnik,” says William McKinnon, a planetary scientist at Washington University in St. Louis, Missouri.

Researchers already knew that Sputnik Planitia (formerly dubbed Sputnik Planum) is made mostly of nitrogen ice, churning and flowing in massive glaciers1. But its sheer size — 1,000 kilometres across and at least several kilometres deep — means that it exerts extraordinary influence over the dwarf planet’s behaviour.

The heart may have even knocked Pluto on its side. At the meeting, James Tuttle Keane of the University of Arizona in Tucson showed how the feature’s formation could have altered Pluto’s tilt. Sputnik Planitia may be a crater punched by a giant meteorite impact, which later filled with ice. The sheer mass of all that ice caused the dwarf planet to rotate relative to its spin axis, Keane says, so that Sputnik Planitia ended up permanently facing away from Pluto’s biggest moon, Charon. “Pluto followed its heart,” he says. (Other scientists, such as Douglas Hamilton of the University of Maryland in College Park, have suggested that Sputnik Planitia might have accumulated ice without an impact, and that the hole instead comes from the sheer weight of the ice depressing the ground beneath it.)

Explaining the Short Rotation Period of Hi'iaka, Haumea's Largest Satellite

The Short Rotation Period of Hi'iaka, Haumea's Largest Satellite

Authors:

Hastings et al

Abstract:

Hi'iaka is the larger outer satellite of the dwarf planet Haumea. Using relative photometry from the Hubble Space Telescope and Magellan and a phase dispersion minimization analysis, we have identified the rotation period of Hi'iaka to be ~9.8 hrs (double-peaked). This is ~120 times faster than its orbital period, creating new questions about the formation of this system and possible tidal evolution. The rapid rotation suggests that Hi'iaka could have a significant obliquity and spin precession that could be visible in light curves within a few years. We then turn to an investigation of what we learn about the (presently unclear) formation of the Haumea system and family based on this unexpectedly rapid rotation rate. We explore the importance of the initial semi-major axis and rotation period in tidal evolution theory and find they strongly influence the time required to despin to synchronous rotation, relevant to understanding a wide variety of satellite and binary systems. We find that despinning tides do not necessarily lead to synchronous spin periods for Hi'iaka, even if it formed near the Roche limit. Therefore the short rotation period of Hi'iaka does not rule out significant tidal evolution. Hi'iaka's spin period is also consistent with formation near its current location and spin up due to Haumea-centric impactors.

New Horizons Imaging of (15810) 1994 JR1 from the Kuiper Belt

The First High-Phase Observations of a KBO: New Horizons Imaging of (15810) 1994 JR1 from the Kuiper Belt

Authors:

Porter et al

Abstract:

NASA's New Horizons spacecraft observed (15810) 1994 JR1, a 3:2 resonant Kupier Belt Object (KBO), using the LOng Range Reconnaissance Imager (LORRI) on November 2, 2015 from a distance of 1.85 AU, and again on April 7, 2016 from a distance of 0.71 AU. These were the first close observations of any KBO other than Pluto. Combining ground-based and Hubble Space Telecope (HST) observations at small phase angles and the LORRI observations at higher phase angles, we produced the first disk-integrated solar phase curve of a typical KBO from α=0.6-58∘. Observations at these geometries, attainable only from a spacecraft in the outer Solar System, constrain surface properties such as macroscopic roughness and the single particle phase function. 1994 JR1 has a rough surface with a 37±5∘ mean topographic slope angle and has a relatively rapid rotation period of 5.47±0.33 hours. 1994 JR1 is currently 2.7 AU from Pluto; our astrometric points enable high-precision orbit determination and integrations which show that it comes this close to Pluto every 2.4 million years (104 heliocentric orbits), causing Pluto to perturb 1994 JR1. During the November spacecraft observation, the KBO was simultaneously observed using HST in two colors, confirming its very red spectral slope. These observations have laid the groundwork for numerous potential future distant KBO observations in the New Horizons-Kuiper Belt Extended Mission.

Are Rings Around Saturn & Other Gas Giants From Shattered Dwarf Planets?

Ring Formation around Giant Planets by Tidal Disruption of a Single Passing Large Kuiper Belt Object

Authors:

Hyodo et al

Abstract:

The origin of rings around giant planets remains elusive. Saturn's rings are massive and made of 90-95% of water ice. In contrast, the much less massive rings of Uranus and Neptune are dark and likely to have higher rock fraction. Here we investigate, for the first time, the tidal disruption of a passing object, including the subsequent formation of planetary rings. First, we perform SPH simulations of the tidal destruction of big differentiated objects (Mbody=1021−23) that experience close encounters with Saturn or Uranus. We find that about 0.1−10% of the mass of the passing body is gravitationally captured around the planet. However, these fragments are initially big chunks and have highly eccentric orbits around the planet. Then, we perform N-body simulations including the planet's oblateness, starting with data obtained from the SPH simulations. Our N-body simulations show that the chunks are tidally destroyed during their next several orbits. Their individual orbits then start to precess incoherently around the planet's equator, which enhances their encounter velocities on longer-term evolution, resulting in more destructive impacts. These collisions would damp their eccentricities resulting in a progressive collapse of the debris cloud into a thin equatorial and low-eccentricity ring. These high energy impacts are expected to be catastrophic enough to produce small particles. Our numerical results also show that the mass of formed rings is large enough to explain current rings including inner regular satellites around Saturn and Uranus. In the case of Uranus, a body can go deeper inside the planet's Roche limit resulting in a more efficient capture of rocky material compared to Saturn's case in which mostly ice is captured. Thus, our results can naturally explain the compositional difference between the rings of Saturn, Uranus and Neptune.

New Horizons Constraints on Charon's Present Day Atmosphere

New Horizons Constraints on Charon's Present Day Atmosphere

Authors:

Stern et al

Abstract:

We report on a variety of standard techniques used by New Horizons including a solar ultraviolet occultation, ultraviolet airglow observations, and high-phase look-back particulate search imaging to search for an atmosphere around Pluto's large moon Charon during its flyby in July 2015. Analyzing these datasets, no evidence for a present day atmosphere has been found for 14 potential atomic and molecular species, all of which are now constrained to have pressures below 0.3 nanobar, as we describe below, these are much more stringent upper limits than the previously available 15-110 nanobar constraints (e.g., Sicardy et al. 2006); for example, we find a 3σ upper limit for an N2 atmosphere on Charon is 4.2 picobars and a 3σ upper limit for the brightness of any atmospheric haze on Charon of I/F=2.6x10−5. A radio occultation search for an atmosphere around Charon was also conducted by New Horizons but will be published separately by other authors.

Cryovolcanism Took Place on Ceres Since the Start of the Triassic

Cryovolcanism on Ceres

Authors:

Ruesch et al

Abstract:

INTRODUCTION

Classic volcanism prevalent on terrestrial planets and volatile-poor protoplanets, such as asteroid Vesta, is based on silicate chemistry and is often expressed by volcanic edifices (unless erased by impact bombardment). In ice-rich bodies with sufficiently warm interiors, cryovolcanism involving liquid brines can occur. Smooth plains on some icy satellites of the outer solar system have been suggested as possibly cryovolcanic in origin. However, evidence for cryovolcanic edifices has proven elusive. Ceres is a volatile-rich dwarf planet with an average equatorial surface temperature of ~160 K. Whether this small (~940 km diameter) body without tidal dissipation could sustain cryovolcanism has been an open question because the surface landforms and relation to internal activity were unknown.

RATIONALE

The Framing Camera onboard the Dawn spacecraft has observed >99% of Ceres’ surface at a resolution of 35 m/pixel at visible wavelengths. This wide coverage and resolution were exploited for geologic mapping and age determination. Observations with a resolution of 135 m/pixel were obtained under several different viewing geometries. The stereo-photogrammetric method applied to this data set allowed the calculation of a digital terrain model, from which morphometry was investigated. The observations revealed a 4-km-high topographic relief, named Ahuna Mons, that is consistent with a cryovolcanic dome emplacement.

RESULTS

The ~17-km-wide and 4-km-high Ahuna Mons has a distinct size, shape, and morphology. Its summit topography is concave downward, and its flanks are at the angle of repose. The morphology is characterized by (i) troughs, ridges, and hummocky areas at the summit, indicating multiple phases of activity, such as extensional fracturing, and (ii) downslope lineations on the flanks, indicating rockfalls and accumulation of slope debris. These morphometric and morphologic observations are explained by the formation of a cryovolcanic dome, which is analogous to a high-viscosity silicic dome on terrestrial planets. Models indicate that extrusions of a highly viscous melt-bearing material can lead to the buildup of a brittle carapace at the summit, enclosing a ductile core. Partial fracturing and disintegration of the carapace generates slope debris, and relaxation of the dome’s ductile core due to gravity shapes the topographic profile of the summit. Modeling of this final phase of dome relaxation and reproduction of the topographic profile requires an extruded material of high viscosity, which is consistent with the mountain’s morphology. We constrained the age of the most recent activity on Ahuna Mons to be within the past 210 ± 30 million years.

CONCLUSION

Cryovolcanic activity during the geologically recent past of Ceres constrains its thermal and chemical history. We propose that hydrated salts with low eutectic temperatures and low thermal conductivities enabled the presence of cryomagmatic liquids within Ceres. These salts are the product of global aqueous alteration, a key process for Ceres’ evolution as recorded by the aqueously altered, secondary minerals observed on the surface.

2015 RR245: a dwarf planet candidate in the 9:2 resonance with Neptune

OSSOS: IV. Discovery of a dwarf planet candidate in the 9:2 resonance

Authors:

Bannister et al

Abstract:

We report the discovery and orbit of a new dwarf planet candidate, 2015 RR245, by the Outer Solar System Origins Survey (OSSOS). 2015 RR245's orbit is eccentric (e=0.586), with a semi-major axis near 82 au, yielding a perihelion distance of 34 au. 2015 RR245 has g−r=0.59±0.11 and absolute magnitude Hr=3.6±0.1; for an assumed albedo of pV=12% the object has a diameter of ∼670 km. Based on astrometric measurements from OSSOS and Pan-STARRS1, we find that 2015 RR245 is securely trapped in the 9:2 mean-motion resonance with Neptune. It is the first TNO identified in this resonance. On hundred-Myr timescales, particles in 2015 RR245-like orbits depart and sometimes return to the resonance, indicating that 2015 RR245 likely forms part of the long-lived metastable population of distant TNOs that drift between resonance sticking and actively scattering via gravitational encounters with Neptune. The discovery of a 9:2 TNO stresses the role of resonances in the long-term evolution of objects in the scattering disk, and reinforces the view that distant resonances are heavily populated in the current Solar System. This object further motivates detailed modelling of the transient sticking population.

2015 RR245: a new Kuiper Belt Dwarf Planet

A new dwarf planet has been discovered beyond Neptune, in the disk of small icy worlds that resides there. The planet was discovered by an international team of astronomers as part of the Outer Solar Systems Origins Survey (OSSOS). The instrument that found it was the Canada-France Hawaii Telescope at Maunakea, Hawaii.

The planet is about 700 km in size, and has been given the name 2015 RR245. It was first sighted by Dr. JJ Kavelaars, of the National Research Council of Canada, in images taken in 2015. Dwarf planets are notoriously difficult to spot, but they’re important pieces of the puzzle in tracing the evolution of our Solar System.

link.

Ceres, we Knew you not

The asteroid belt hides lots of mysteries of the solar system’s past, but perhaps no place holds more mysteries than Ceres. It’s an oddball place — a dwarf planet in the midst of our solar system’s belt of smaller debris. And it’s an ancient world possibly left over from the era when the planets first came together.

link.

Dwarf Planet 2007 OR10 Much Larger Than Originally Thought

According to a team of astronomers making use of data from two powerful orbital telescopes, a dwarf planet known as 2007 OR10 orbiting in the far reaches of our solar system is significantly larger than previously believed. The results of the study makes the little-known planetoid the third largest dwarf planet behind Pluto and Eris.

Previous observations of 2007 OR10 using only infrared data from the Herschel telescope had estimated the dwarf planet to have a diameter of around 795 miles (1,280 km). However, these readings were taken without knowledge of 2007 OR10's rotational period, which is a key variable needed for astronomers to extrapolate the size of a heavenly body.

Without this key variable, the light detected by a telescope could lead to incorrect estimations of a planetoid's size, as was the case with 2007 OR10. A smaller body with a brighter surface could potentially appear larger than a darker, much larger dwarf planet.

The new research paired infrared readings collected by Herschel with visible light data harvested by the Kepler spacecraft, which was tasked with observing 2007 OR10 for a continuous period of 19 days in late 2014. The combination of the data sets allowed astronomers to deduce a number of characteristics of the distant planetoid.

link.

Hunting for Moons of Dwarf Planet Haumea

A Deep Search for Additional Satellites around the Dwarf Planet Haumea

Authors:

Burkhart et al

Abstract:

Haumea is a dwarf planet with two known satellites, an unusually high spin rate, and a large collisional family, making it one of the most interesting objects in the outer solar system. A fully self-consistent formation scenario responsible for the satellite and family formation is still elusive, but some processes predict the initial formation of many small moons, similar to the small moons recently discovered around Pluto. Deep searches for regular satellites around KBOs are difficult due to observational limitations, but Haumea is one of the few for which sufficient data exist. We analyze Hubble Space Telescope (HST) observations, focusing on a ten-consecutive-orbit sequence obtained in July 2010, to search for new very small satellites. To maximize the search depth, we implement and validate a non-linear shift-and-stack method. No additional satellites of Haumea are found, but by implanting and recovering artificial sources, we characterize our sensitivity. At distances between ∼10,000 km and ∼350,000 km from Haumea, satellites with radii as small as ∼10 km are ruled out, assuming an albedo (p≃0.7) similar to Haumea. We also rule out satellites larger than ≳40 km in most of the Hill sphere using other HST data. This search method rules out objects similar in size to the small moons of Pluto. By developing clear criteria for determining the number of non-linear rates to use, we find that far fewer shift rates are required (∼35) than might be expected. The non-linear shift-and-stack method to discover satellites (and other moving transients) is tractable, particularly in the regime where non-linear motion begins to manifest itself.

What Mechanism is Causing the Kuiper Belt Objects by Planet Nine?

Orbital clustering of distant Kuiper Belt Objects by hypothetical Planet 9. Secular or resonant ?

Authors:

Beust et al

Abstract:

Statistical analysis of the orbits of distant Kuiper Belt Objects (KBOs) have led to suggest that an additional planet should reside in the Solar System. According to recent models, the secular action of this body should cause orbital alignment of the KBOs. It was recently claimed that the KBOs concerned by this dynamics are presumably trapped in mean motion resonances with the suspected planet. I reinvestigate here the secular model underlying this idea. The original analysis was done expanding and truncating the secular Hamiltonian. I show that this is inappropriate here, as the series expansion is not convergent. I present a study based on numerical computation of the Hamiltonian with no expansion. I show in phase-space diagrams the existence of apsidally anti-aligned, high eccentricity libration islands that were not present in the original modelling, but that match numerical simulations. These island were claimed to correspond to bodies trapped in mean-motion resonances with the hypothetical planet, and match the characteristics of the distant KBOs observed. My main result is that regular secular dynamics can account for the anti-aligned particles itself as well as mean-motion resonances. I also perform a semi-analytical study of resonant motion and show that some resonance are actually capable of producing the same libration islands. I discuss then the relative importance of both mechanisms.

Interpreting the Densities of the Kuiper Belt’s Dwarf Planets

Interpreting the Densities of the Kuiper Belt’s Dwarf Planets

Authors:

Barr et al

Abstract:

Kuiper Belt objects with absolute magnitude less than 3 (radius ≳500 km), the dwarf planets, have a range of different ice/rock ratios, and are more rock-rich than their smaller counterparts. Many of these objects have moons, which suggests that collisions may have played a role in modifying their compositions. We show that the dwarf planets fall into two categories when analysed by their mean densities and satellite-to-primary size ratio. Systems with large moons, such as Pluto/Charon and Orcus/Vanth, can form in low-velocity grazing collisions in which both bodies retain their compositions. We propose that these systems retain a primordial composition, with a density of about 1.8 g/cm3. Triton, thought to be a captured KBO, could have lost enough ice during its early orbital evolution to explain its rock-enrichment relative to the primordial material. Systems with small moons, Eris, Haumea, and Quaoar, formed from a different type of collision in which icy material, perhaps a few tens of percent of the total colliding mass, is lost. The fragments would not remain in physical or dynamical proximity to the parent body. The ice loss process has not yet been demonstrated numerically, which could be due to the paucity of KBO origin simulations, or missing physical processes in the impact models. If our hypothesis is correct, we predict that large KBOs with small moons should be denser than the primordial material, and that the mean density of Orcus should be close to the primordial value.

Pluto's Bladed Terrain in 3d

link.

Looking at Ceres

At last week's Lunar and Planetary Science Conference, I enjoyed a large number of talks about Ceres, which Dawn is now orbiting at an altitude of merely 385 kilometers. Several sessions worth of talks considered a wealth of new data that has been acquired since the last time I attended scientific sessions on Dawn, at lower altitudes and hence more detail. All that freshly acquired data made for talks bursting with pretty pictures and data but relatively thin on interpretation and with little coordination (yet) across data sets, which makes them a bit hard to summarize briefly. Deputy principal investigator Carol Raymond summed the situation up well at the press briefing: "Clearly, we have a lot of work to do to put together a self-consistent story among all these different data sets."

link.

Frozen Nitrogen Lake, Channels Spotted on Pluto

NASA's New Horizons spacecraft spied several features on Pluto that offer evidence of a time millions or billions of years ago when – thanks to much higher pressure in Pluto's atmosphere and warmer conditions on the surface – liquids might have flowed across and pooled on the surface of the distant world.

"In addition to this possible former lake, we also see evidence of channels that may also have carried liquids in Pluto's past," said Alan Stern, Southwest Research Institute, Boulder, Colorado—principal investigator of New Horizons and lead author of the scientific paper.

This feature appears to be a frozen, former lake of liquid nitrogen, located in a mountain range just north of Pluto's informally named Sputnik Planum. Captured by the New Horizons' Long Range Reconnaissance Imager (LORRI) as the spacecraft flew past Pluto on July 14, 2015, the image shows details as small as about 430 feet (130 meters). At its widest point the possible lake appears to be about 20 miles (30 kilometers) across.

link.

Interpreting the Densities of the Kuiper Belt's Dwarf Planets

Interpreting the Densities of the Kuiper Belt's Dwarf Planets

Authors:

Barr et al

Abstract:

Kuiper Belt objects with absolute magnitude less than 3 (radius ≳500 km), the dwarf planets, have a range of different ice/rock ratios, and are more rock-rich than their smaller counterparts. Many of these objects have moons, which suggests that collisions may have played a role in modifying their compositions. We show that the dwarf planets fall into two categories when analysed by their mean densities and satellite-to-primary size ratio. Systems with large moons, such as Pluto/Charon and Orcus/Vanth, can form in low-velocity grazing collisions in which both bodies retain their compositions. We propose that these systems retain a primordial composition, with a density of about 1.8 g/cm3. Triton, thought to be a captured KBO, could have lost enough ice during its early orbital evolution to explain its rock-enrichment relative to the primordial material. Systems with small moons, Eris, Haumea, and Quaoar, formed from a different type of collision in which icy material, perhaps a few tens of percent of the total colliding mass, is lost. The fragments would not remain in physical or dynamical proximity to the parent body. The ice loss process has not yet been demonstrated numerically, which could be due to the paucity of KBO origin simulations, or missing physical processes in the impact models. If our hypothesis is correct, we predict that large KBOs with small moons should be denser than the primordial material, and that the mean density of Orcus should be close to the primordial value.