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Register a new userThe size, shape, density and ring of the dwarf planet Haumea from a stellar occultation
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Added by
Estela Fern\\'andez-Valenzuela
Publication date
2020
fields
Physics
and research's language is
English
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Among the four known transneptunian dwarf planets, Haumea is an exotic, very elongated, and fast rotating body. In contrast to the other dwarf planets, its size, shape, albedo, and density are not well constrained. Here we report results of a multi-chord stellar occultation, observed on 2017 January 21. Secondary events observed around the main body are consistent with the presence of a ring of opacity 0.5, width 70 km, and radius 2,287$_{-45}^{+75}$ km. The Centaur Chariklo was the first body other than a giant planet to show a ring system and the Centaur Chiron was later found to possess something similar to Chariklos rings. Haumea is the first body outside the Centaur population with a ring. The ring is coplanar with both Haumeas equator and the orbit of its satellite Hiiaka. Its radius places close to the 3:1 mean motion resonance with Haumeas spin period. The occultation by the main body provides an instantaneous elliptical limb with axes 1,704 $pm$ 4 km x 1,138 $pm$ 26 km. Combined with rotational light-curves, it constrains Haumeas 3D orientation and its triaxial shape, which is inconsistent with a homogeneous body in hydrostatic equilibrium. Haumeas largest axis is at least 2,322 $pm$ 60 km, larger than thought before. This implies an upper limit of 1,885 $pm$ 80 kg m$^{-3}$ for Haumeas density, smaller and less puzzling than previous estimations, and a geometric albedo of 0.51 $pm$ 0.02, also smaller than previous estimations. No global N$_2$ or CH$_4$ atmosphere with pressures larger than 15 and 50 nbar (3-$sigma$ limits), respectively, is detected.
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The recently discovered ring around the dwarf planet (136108) Haumea is located near the 1:3 resonance between the orbital motion of the ring particles and the spin of Haumea. In the current work is studied the dynamics of individual particles in the region where is located the ring. Using the Poincare Surface of Section technique, the islands of stability associated with the 1:3 resonance are identified and studied. Along all its existence this resonance showed to be doubled, producing pairs of periodic and quasi-periodic orbits. The fact of being doubled introduces a separatrix, which generates a chaotic layer that significantly reduces the size of the stable regions of the 1:3 resonance. The results also show that there is a minimum equivalent eccentricity ($e_{1:3}$) for the existence of such resonance. This value seems to be too high to keep a particle within the borders of the ring. On the other hand, the Poincare Surface of Sections show the existence of much larger stable regions, but associated with a family of first kind periodic orbits. They exist with equivalent eccentricity values lower than $e_{1:3}$, and covering a large radial distance, which encompasses the region of the Haumeas ring. Therefore, this analysis suggests the Haumeas ring is in a stable region associated with a first kind periodic orbit instead of the 1:3 resonance.
We present the results from four stellar occultations by (486958) Arrokoth, the flyby target of the New Horizons extended mission. Three of the four efforts led to positive detections of the body, and all constrained the presence of rings and other debris, finding none. Twenty-five mobile stations were deployed for 2017 June 3 and augmented by fixed telescopes. There were no positive detections from this effort. The event on 2017 July 10 was observed by SOFIA with one very short chord. Twenty-four deployed stations on 2017 July 17 resulted in five chords that clearly showed a complicated shape consistent with a contact binary with rough dimensions of 20 by 30 km for the overall outline. A visible albedo of 10% was derived from these data. Twenty-two systems were deployed for the fourth event on 2018 Aug 4 and resulted in two chords. The combination of the occultation data and the flyby results provides a significant refinement of the rotation period, now estimated to be 15.9380 $pm$ 0.0005 hours. The occultation data also provided high-precision astrometric constraints on the position of the object that were crucial for supporting the navigation for the New Horizons flyby. This work demonstrates an effective method for obtaining detailed size and shape information and probing for rings and dust on distant Kuiper Belt objects as well as being an important source of positional data that can aid in spacecraft navigation that is particularly useful for small and distant bodies.
We present here HST NICMOS F110W and F160W observations of Haumea, and its two satellites Hiiaka and Namaka. From the measured (F110W-F160W) colours of -1.209 +/-0.004, -1.48 +/- 0.06, and -1.4 +/- 0.2 mag for each object, respectively, we infer that the 1.6 imcron water-ice absorption feature depths on Hiiaka and Namaka are at least as deep as that of Haumea. The light-curve of Haumea is detected in both filters, and we find that the infrared colour is bluer by approximately 2-3% at the phase of the red spot. These observations suggest that the satellites of Haumea were formed from the collision that produced the Haumea collisional family.
Haumea, a rapidly rotating elongated dwarf planet (~ 1500 km in diameter), has two satellites and is associated with a family of several smaller Kuiper Belt objects (KBOs) in similar orbits. All members of the Haumea system share a water ice spectral feature that is distinct from all other KBOs. The relative velocities between the Haumea family members are too small to have formed by catastrophic disruption of a large precursor body, which is the process that formed families around much smaller asteroids in the Main Belt. Here we show that all of the unusual characteristics of the Haumea system are explained by a novel type of giant collision: a graze-and-merge impact between two comparably sized bodies. The grazing encounter imparted the high angular momentum that spun off fragments from the icy crust of the elongated merged body. The fragments became satellites and family members. Giant collision outcomes are extremely sensitive to the impact parameters. Compared to the Main Belt, the largest bodies in the Kuiper Belt are more massive and experience slower velocity collisions; hence, outcomes of giant collisions are dramatically different between the inner and outer solar system. The dwarf planets in the Kuiper Belt record an unexpectedly large number of giant collisions, requiring a special dynamical event at the end of solar system formation.
We report the latest Planet Hunter results, including PH2 b, a Jupiter-size (R_PL = 10.12 pm 0.56 R_E) planet orbiting in the habitable zone of a solar-type star. PH2 b was elevated from candidate status when a series of false positive tests yielded a 99.9% confidence level that transit events detected around the star KIC 12735740 had a planetary origin. Planet Hunter volunteers have also discovered 42 new planet candidates in the Kepler public archive data, of which 33 have at least three transits recorded. Most of these transit candidates have orbital periods longer than 100 days and 20 are potentially located in the habitable zones of their host stars. Nine candidates were detected with only two transit events and the prospective periods are longer than 400 days. The photometric models suggest that these objects have radii that range between Neptune to Jupiter. These detections nearly double the number of gas giant planet candidates orbiting at habitable zone distances. We conducted spectroscopic observations for nine of the brighter targets to improve the stellar parameters and we obtained adaptive optics imaging for four of the stars to search for blended background or foreground stars that could confuse our photometric modeling. We present an iterative analysis method to derive the stellar and planet properties and uncertainties by combining the available spectroscopic parameters, stellar evolution models, and transiting light curve parameters, weighted by the measurement errors. Planet Hunters is a citizen science project that crowd-sources the assessment of NASA Kepler light curves. The discovery of these 43 planet candidates demonstrates the success of citizen scientists at identifying planet candidates, even in longer period orbits with only two or three transit events.
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