Collision With a 2 Earth Mass Planet Shaped Uranus' Evolution

Uranus was hit by a massive object roughly twice the size of Earth that caused the planet to tilt and could explain its freezing temperatures, according to new research.

Astronomers at Durham University, UK, led an international team of experts to investigate how Uranus came to be tilted on its side and what consequences a giant impact would have had on the planet's evolution.

The team ran the first high-resolution computer simulations of different massive collisions with the ice giant to try to work out how the planet evolved.

The research confirms a previous study which said that Uranus' tilted position was caused by a collision with a massive object - most likely a young proto-planet made of rock and ice - during the formation of the solar system about 4 billion years ago.

The simulations also suggested that debris from the impactor could form a thin shell near the edge of the planet's ice layer and trap the heat emanating from Uranus' core. The trapping of this internal heat could in part help explain Uranus' extremely cold temperature of the planet's outer atmosphere (-216 degrees Celsius, -357 degrees Fahrenheit), the researchers said.

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Europa Lander Being Redesigned for Lowering Cost

Revised concepts for a proposed Europa lander mission could reduce its mass and cost by simplifying its science requirements and doing away with a dedicated communications relay.

In a presentation at a meeting of the Committee on Astrobiology and Planetary Science of the National Academies March 28, Kevin Hand of the Jet Propulsion Laboratory said that feedback from a mission concept review for the proposed lander last June led to changes in the design to reduce its cost.

“The technology and science were well received. The marching orders that we got out of that review were to see if we could simplify the architecture to reduce complexity and cost,” he said. While there’s been little discussion of the lander’s cost, Hand said there was a “desire” to reduce its cost to below $3 billion.

The concept for the mission presented at that review involved the launch of the lander on a Space Launch System rocket no earlier than late 2025. The spacecraft would enter orbit around Jupiter in 2030 with a landing on Europa to follow no earlier than December 2031. The battery-powered lander would operate on the surface for at least 20 days, relying on a communications relay spacecraft in orbit to return data to Earth.

Hand said the project team looked at options to do away with the relay spacecraft by giving the lander a larger antenna to enable direct-to-Earth communications. That concept uses a flat-panel antenna 80 centimeters across, versus antenna smaller antennas 30 to 40 centimeters across intended for communications with the relay. One quadrant of that larger antenna has been built and tested at JPL, he said, with “encouraging” results.

Another factor that enables the change in design, he said, is a shift in the science requirements for the lander. A report by a science definition team last year had included, as one of the mission’s priorities, the ability of the lander’s instruments to directly detect any life that might exist in the moon’s icy surface.

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WISE & NEOWISE Cannot Find Planet Nine

A 3pi Search for Planet Nine at 3.4 microns with WISE and NEOWISE

Authors:

Meisner et al

Abstract:
The recent 'Planet Nine' hypothesis has led to many observational and archival searches for this giant planet proposed to orbit the Sun at hundreds of astronomical units. While trans-Neptunian object searches are typically conducted in the optical, models suggest Planet Nine could be self-luminous and potentially bright enough at ~3-5 microns to be detected by the Wide-field Infrared Survey Explorer (WISE). We have previously demonstrated a Planet Nine search methodology based on time-resolved WISE coadds, allowing us to detect moving objects much fainter than would be possible using single-frame extractions. In the present work, we extend our 3.4 micron (W1) search to cover more than three quarters of the sky and incorporate four years of WISE observations spanning a seven year time period. This represents the deepest and widest-area WISE search for Planet Nine to date. We characterize the spatial variation of our survey's sensitivity and rule out the presence of Planet Nine in the parameter space searched at W1 less than 16.7 in high Galactic latitude regions (90% completeness).

Fly Over Pluto

Video is based on data and images from New Horizons.

systematic is Hunting for Planet Nine

A year ago, last January, Konstantin Batygin and Mike Brown lit up the Internet with their dossier of evidence for Planet Nine. Their conclusion was electrifying: An as-yet undetected super-Earth may be lurking a light week away in an eccentric orbit far beyond Neptune. Their article in the Astronomical Journal generated intense interest, including 311,371 (and counting) downloads of a .pdf containing a bracing dose of secular perturbation theory, along with push notifications from the likes of the New York Times and NPR to devices worldwide.

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New Horizons Prepares for Encounter With Kuiper Belt Object 2014 MU69

A year and a half after its historic flyby of dwarf planet Pluto, NASA’s New Horizons spacecraft is preparing for its encounter with a second Kuiper Belt Object. Now just two years away from the planned 1 January 2019 encounter with 2014 MU69, New Horizons is in a healthy state as it sails toward the small, rocky, classical Kuiper Belt Object.

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Where Planet Nine Might be Hiding

Constraints on Planet Nine's Orbit and Sky Position within a Framework of Mean Motion Resonances

Authors:

Millholland et al

Abstract:

A number of authors have proposed that the statistically significant orbital alignment of the most distant Kuiper Belt Objects (KBOs) is evidence of an as-yet undetected planet in the outer solar system, now referred to colloquially a "Planet Nine". Dynamical simulations by Batygin & Brown (2016) have provided constraints on the range of the planet's possible orbits and sky locations. We extend these investigations by exploring the suggestion of Malhotra et al. (2016) that Planet Nine is in small integer ratio mean-motion resonances (MMRs) with several of the most distant KBOs. We show that the observed KBO semi-major axes present a set of commensurabilities with an unseen planet at ∼654 AU (P∼16,725 yr) that has a greater than 98% chance of stemming from a sequence of MMRs rather than from a random distribution. We describe and implement a Monte-Carlo optimization scheme that drives billion-year dynamical integrations of the outer solar system to pinpoint the orbital properties of perturbers that are capable of maintaining the KBOs' apsidal alignment. This optimization exercise suggests that the unseen planet is most consistently represented with mass, m∼6−12M⊕, semi-major axis, a∼654 AU, eccentricity, e∼0.45, inclination, i∼30∘, argument of periastron, ω∼150∘, longitude of ascending node, Ω∼50∘, and mean anomaly, M∼180∘. A range of sky locations relative to this fiducial ephemeris are possible. We find that the region 30∘≲RA≲50∘, −20∘≲Dec≲20∘ is promising.

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.

Hunting for Planet Nine With Wise & NEOWise

Searching for Planet Nine with Coadded WISE and NEOWISE-Reactivation Images

Authors:

Meisner et al

Abstract:

A distant, as yet unseen ninth planet has been invoked to explain various observations of the outer solar system. While such a 'Planet Nine', if it exists, is most likely to be discovered via reflected light in the optical, it may emit much more strongly at 3−5μm than simple blackbody predictions would suggest, depending on its atmospheric properties (Fortney et al. 2016). As a result, Planet Nine may be detectable at 3.4μm with WISE, but single exposures are too shallow except at relatively small distances (d9≲430 AU). We develop a method to search for Planet Nine far beyond the W1 single-exposure sensitivity, to distances as large as 800 AU, using inertial coadds of W1 exposures binned into ∼1 day intervals. We apply our methodology to ∼2000 square degrees of sky identified by Holman & Payne (2016) as a potentially likely Planet Nine location, based on the Fienga et al. (2016) Cassini ranging analysis. We do not detect a plausible Planet Nine candidate, but are able to derive a detailed completeness curve, ruling out its presence within the parameter space searched at W1<16.66 (90% completeness). Our method uses all publicly available W1 imaging, spanning 2010 January to 2015 December, and will become more sensitive with future NEOWISE-Reactivation releases of additional W1 exposures. We anticipate that our method will be applicable to the entire high Galactic latitude sky, and we will extend our search to that full footprint in the near future.

Planet Nine may be Especially Faint in the red and Infrared

Comprehensive wide-band magnitudes and albedos for the planets, with applications to exo-planets and Planet Nine

Authors:

Mallama et al

Abstract:

Complete sets of reference magnitudes in all 7 Johnson-Cousins bands (U, B, V, R, I, RC and IC) and the 5 principal Sloan bands (u’, g’, r’, i', and z’) are presented for the 8 planets. These data are accompanied by illumination phase functions and other formulas which characterize the instantaneous brightness of the planets. The main source of Johnson-Cousins magnitudes is a series of individualized photometric studies reported in recent years. Gaps in that dataset were filled with magnitudes synthesized in this study from published spectrophotometry. The planetary Sloan magnitudes, which are established here for the first time, are an average of newly recorded Sloan filter photometry, synthetic magnitudes and values transformed from the Johnson-Cousins system. Geometric albedos derived from these two sets of magnitudes are consistent within each photometric system and between the systems for all planets and in all bands. This consistency validates the albedos themselves as well as the magnitudes from which they were derived. In addition, a quantity termed the delta stellar magnitude is introduced to indicate the difference between the magnitude of a planet and that of its parent star. A table of these delta values for exo-planets possessing a range of physical characteristics is presented. The delta magnitudes are for phase angle 90° where a planet is near the greatest apparent separation from its star. This quantity may be useful in exo-planet detection and observation strategies when an estimate of the signal-to-noise ratio is needed. Likewise, the phase curves presented in this paper can be used for characterizing exo-planets. Finally, magnitudes for the proposed Planet Nine are estimated, and we note that P9 may be especially faint at red and near-IR wavelengths.

Doubts About Planet Nine?

Consequences of a Distant Massive Planet on the Large Semi-major Axis Trans-Neptunian Objects

Authors:

Shankman et al

Abstract:

We explore the distant giant planet hypothesis by integrating the large semi-major axis, large pericenter Trans-Neptunian Objects (TNOs) in the presence of the giant planets and an external perturber whose orbit is consistent with the proposed distant, eccentric, and inclined giant planet, so called planet 9. We find that TNOs with semi-major axes greater than 250 au experience some longitude of perihelion shepherding, but that a generic outcome of such evolutions is that the TNOs evolve to larger pericenter orbits, and commonly get raised to retrograde inclinations. This pericenter and inclination evolution requires a massive disk of TNOs (tens of M$_\Earth$) in order to explain the detection of the known sample today. Some of the highly inclined orbits produced by the examined perturbers will be inside of the orbital parameter space probed by prior surveys, implying a missing signature of the 9th planet scenario. The distant giant planet scenarios explored in this work do not reproduce the observed signal of simultaneous clustering in argument of pericenter, longitude of the ascending node, and longitude of perihelion in the region of the known TNOs.

Shaping of the inner Oort cloud by Planet Nine

Shaping of the inner Oort cloud by Planet Nine

Authors:

Michaely et al

Abstract:

We present a numerical calculation of the dynamical interaction between the proposed Planet Nine and an initially thin circular debris disk around the Sun for 4Gyr, accounting the secular perturbation of the four giant planets. We show that Planet Nine governs the dynamics in between 1000-5000AU and forms spherical structure in the inner part (~1000AU) surrounded by an inclined disk aligned to its orbital plane. This structure is the outcome of mean motion resonances and secular interaction with Planet Nine. We compare the morphology of this structure with the outcome from a fly-by encounter of a star with the debris disk and show distinct differences between the two scenarios. We predict that this structure serves as a source of comets and calculate the resulting comet production rate to be detectable.

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 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.

Niku: a Retrograde Orbiting Trans Neptunian Object

Discovery of A New Retrograde Trans-Neptunian Object: Hint of A Common Orbital Plane for Low Semi-Major Axis, High Inclination TNOs and Centaurs

Authors:

Chen et al

Abstract:

Although the majority of Centaurs are thought to have originated in the scattered disk, with the high-inclination members coming from the Oort cloud, the origin of the high inclination component of trans-Neptunian objects (TNOs) remains uncertain. We report the discovery of a retrograde TNO, which we nickname "Niku", detected by the Pan-STARRS 1 Outer Solar System Survey. Our numerical integrations show that the orbital dynamics of Niku are very similar to that of 2008 KV42 (Drac), with a half-life of ∼500 Myr. Comparing similar high inclination TNOs and Centaurs (q>10 AU, a<100 and="" au="" i="">60∘), we find that these objects exhibit a surprising clustering of ascending node, and occupy a common orbital plane. This orbital configuration has high statistical significance: 3.8-σ. An unknown mechanism is required to explain the observed clustering. This discovery may provide a pathway to investigate a possible reservoir of high-inclination objects.

The Hunt for Planet Nine Finds Multiple Outer Solar System Objects

In the race to discover a proposed ninth planet in our Solar System, Carnegie's Scott Sheppard and Chadwick Trujillo of Northern Arizona University have observed several never-before-seen objects at extreme distances from the Sun in our Solar System. Sheppard and Trujillo have now submitted their latest discoveries to the International Astronomical Union's Minor Planet Center for official designations. A paper about the discoveries has also been accepted to The Astronomical Journal.

The more objects that are found at extreme distances, the better the chance of constraining the location of the ninth planet that Sheppard and Trujillo first predicted to exist far beyond Pluto (itself no longer classified as a planet) in 2014. The placement and orbits of small, so-called extreme trans-Neptunian objects, can help narrow down the size and distance from the Sun of the predicted ninth planet, because that planet's gravity influences the movements of the smaller objects that are far beyond Neptune. The objects are called trans-Neptunian because their orbits around the Sun are greater than Neptune's.

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Microbial Morphology and Motility as Biosignatures for Outer Planet Missions

Microbial Morphology and Motility as Biosignatures for Outer Planet Missions

Authors:

Jay et al

Abstract:

Meaningful motion is an unambiguous biosignature, but because life in the Solar System is most likely to be microbial, the question is whether such motion may be detected effectively on the micrometer scale. Recent results on microbial motility in various Earth environments have provided insight into the physics and biology that determine whether and how microorganisms as small as bacteria and archaea swim, under which conditions, and at which speeds. These discoveries have not yet been reviewed in an astrobiological context. This paper discusses these findings in the context of Earth analog environments and environments expected to be encountered in the outer Solar System, particularly the jovian and saturnian moons. We also review the imaging technologies capable of recording motility of submicrometer-sized organisms and discuss how an instrument would interface with several types of sample-collection strategies.

If Planet Nine Exists, it Could be a 'Disaster' After the Sun Dies

The solar system could be thrown into disaster when the sun dies if the mysterious 'Planet Nine' exists, according to research from the University of Warwick.

Dr Dimitri Veras in the Department of Physics has discovered that the presence of Planet Nine - the hypothetical planet which may exist in the outer Solar System - could cause the elimination of at least one of the giant planets after the sun dies, hurling them out into interstellar space through a sort of 'pinball' effect.

When the sun starts to die in around seven billion years, it will blow away half of its own mass and inflate itself -- swallowing the Earth -- before fading into an ember known as a white dwarf. This mass ejection will push Jupiter, Saturn, Uranus and Neptune out to what was assumed a safe distance.

However, Dr. Veras has discovered that the existence of Planet Nine could rewrite this happy end-ing. He found that Planet Nine might not be pushed out in the same way, and in fact might instead be thrust inward into a death dance with the solar system's four known giant planets -- most notably Uranus and Neptune. The most likely result is ejection from the solar system, forever.

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Could Planet Nine be Causing Solar Obliquity Changes?

Solar Obliquity Induced by Planet Nine: Simple Calculation

Authors:

Lai et al

Abstract:

Bailey et al.~(2016) and Gomes et al.~(2016) recently suggested that the 6 degree misalignment between the Sun's rotational equator and the orbital plane of the major planets may be produced by the forcing from the hypothetical Planet Nine on an inclined orbit. Here we present a simple but accurate calculation of the effect, which provides a clear description of how the Sun's spin orientation depends on the property of Planet Nine in this scenario.

The Upper Limits For Oort Cloud Comets Based on X Ray Astronomy Observations

Upper limits to the number of Oort Cloud Objects based on serendipitous occultation events search in X-rays

Authors:

Chang et al

Abstract:

Using all the RXTE archival data of Sco X-1 and GX 5-1, which amount to about 1.6 mega seconds in total, we searched for possible occultation events caused by Oort Cloud Objects. The detection efficiency of our searching approach was studied with simulation. Our search is sensitive to object size of about 300 m in the inner Oort Cloud, taking 4000 AU as a representative distance, and of 900 m in the outer Oort Cloud, taking 36000 AU as the representative distance. No occultation events were found in the 1.6 Ms data. We derived upper limits to the number of Oort Cloud Objects, which are about three orders of magnitude higher than the highest theoretical estimates in the literature for the inner Oort Cloud, and about six orders higher for the outer Oort Cloud. Although these upper limits are not constraining enough, they are the first obtained observationally, without making any model assumptions about comet injection. They also provide guidance to such serendipitous occultation event search in the future.