Asteroid (3200) Phaethon is an active near-Earth asteroid and the parent body of the Geminid Meteor Shower. Because of its small perihelion distance, Phaethon's surface reaches temperatures sufficient to destabilize hydrated materials. We conducted rotationally resolved spectroscopic observations of this asteroid, mostly covering the northern hemisphere and the equatorial region, beyond 2.5-micron to search for evidence of hydration on its surface. Here we show that the observed part of Phaethon does not exhibit the 3-micron hydrated mineral absorption (within 2-sigma). These observations suggest that Phaethon's modern activity is not due to volatile sublimation or devolatilization of phyllosilicates on its surface. It is possible that the observed part of Phaethon was originally hydrated and has since lost volatiles from its surface via dehydration, supporting its connection to the Pallas family, or it was formed from anhydrous material.
The polarimetric observations of asteroid 3200 Phaethon, the target of international observation campaign, did not cover a proper phase angle interval to provide estimating all the attributes of the asteroid polarization curve. Based on present discrete observation data for Phaethon, its full polarimetric curves in BVRI bandpasses were reproduced. The polarimetric properties of the asteroid correspond to a notion on surface structure as thermally altered regolith particles mixed with lager rock fragments like a coarse pebble.
The main aim of photometrical observations of the asteroid 3200 Phaethon was searching for its low-level cometary activity (possible coma and/or dust tail) in the pre-perihelion passage. We performed observational runs with telescopes ranging from 0.61-m to 2-m and BVR color imaging. Three longer photometric series were used for modeling of the 3D shape of Phaethon. The color indices and size of the asteroid were estimated.
Thermal infrared emission and thermophysical modeling techniques are powerful tools in deciphering the surface properties of asteroids. The near-Earth asteroid (3200) Phaethon is an active asteroid with a very small perihelion distance and is likely the source of the Geminid meteor shower. We estimate and interpret the thermal inertia of this extraordinary asteroid using observations that span ten distinct sightings. The variation in thermal inertia over these sightings is inconsistent with the expected temperature-dependent thermal inertia theorized from radiative heat transfer within the reg…
We report on a multi-observatory campaign to examine asteroid 3200 Phaethon during its December 2017 close approach to Earth, in order to improve our measurements of its fundamental parameters, and to search for surface variations, cometary activity and fragmentation. The mean colors of Phaethon are B-V = 0.702 +/- 0.004, V-R = 0.309 +/- 0.003, R-I = 0.266 +/- 0.004, neutral to slightly blue, consistent with previous classifications of Phaethon as a F-type or B-type asteroid. Variations in Phaethon's B-V colors (but not V-R or R-I) with observer sub-latitude are seen and may be associated with…
We present results of polarimetric, photometric, and spectral observations of the near-Earth asteroid (3200) Phaethon carried out at the 6-m BTA telescope of the Special Astrophysical Observatory and the 2.6-m and 1.25-m telescopes of the Crimean Astrophysical Observatory over a wide range of phase angles during its close approach to the Earth at the end of 2017 (19-135 deg) and in 2020 at α= 52.2 deg. Using our and other available in literature data, we found that the maximum degree of linear polarization of Phaethon in the V band is 45% at the phase angle 124 deg. Using the dependence (polar…
Asteroid (3200) Phaethon, a B-type asteroid, has been active during its perihelion passages. This asteroid is considered to be a source of the Geminid meteor stream. It is reported that this asteroid is spinning at a rotation period of $3.60 \ hr$ and has a top shape (an oblate body with an equatorial ridge) with a mean equatorial diameter of $6.25 \ km$. Here, we report that Phaethon's rotation state may be close to or above its critical rotation period when the bulk density is $0.5 \ - \ 1.5 \ {g/cm^3}$ (a typical bulk density of a B-type asteroid). We found that in this condition, the struc…
A multi-colour phase-polarization curve of asteroid (3200)~Phaethon has been obtained during the December 2017 apparition by merging measurements taken at the observing station of Calern (France) and at the Rhozen observatory (Bulgaria). All the observations were obtained in the positive polarization branch, the phase angle ranging from 36$^\circ$ to 116$^\circ$. The measured values of linear polarization are among the highest ever observed for a Solar system body. The covered interval of phase angle was not sufficiently extended to derive a firm determination of the $P_{\rm max}$ parameter, b…
The asteroid (3200) Phaethon is known to be the parent body of the Geminids, although meteor showers are commonly associated with the activity of periodic comets. What is most peculiar to the asteroid is its comet-like activity in the ejection of micrometer-sized dust particles at every perihelion passage, while the activity of the asteroid has never been identified outside the near-perihelion zone at $0.14~\mathrm{au}$ from the Sun. From the theoretical point of view, we argue that the activity of the asteroid is well explained by the electrostatic lofting of micrometer-sized dust particles w…
We report Arecibo S-band (2380 MHz; 12.6 cm) radar observations of near-Earth asteroid (3200) Phaethon during the December 2017 apparition when Phaethon passed within 0.07 au of Earth. Radar images with a resolution of 75 m per pixel reveal a roughly spheroidal shape more than 6 km in diameter at the equator with several discernible surface features hundreds of meters in extent. These include a possible crater more than 1 km across located below 30$^{\circ}$ latitude and a roughly 600-m radar-dark region near one of the poles. Overall, the radar images of Phaethon are reminiscent of those of (…
Asteroid (3200) Phaethon is a Near-Earth Apollo asteroid with an unusual orbit that brings it closer to the Sun than any other known asteroid. Its last close approach to the Earth was in mid-December 2017 and the next one will be on October 2026. Previous rotationally time-resolved spectroscopy of Phaethon showed that its spectral slope is slightly bluish, in agreement with its B/F taxonomic classification, but at some rotational phases, it changes to slightly reddish. Motivated by this result we performed time-resolved imaging polarimetry of Phaethon during its recent close approach to the Ea…
We present space-based thermal infrared observations of the presumably Geminid-associated asteroids: (3200)Phaethon, 2005 UD and 1999 YC using WISE/NEOWISE. The images were taken at the four wavelength bands 3.4$μ$m(W1),4.6$μ$m(W2),12$μ$m(W3),and 22$μ$m(W4). We find no evidence of lasting mass-loss in the asteroids over the decadal multi-epoch datasets. We set an upper limit to the mass-loss rate in dust of Q<2kg s$^{-1}$ for Phaethon and <0.1kg s$^{-1}$ for both 2005 UD and 1999 YC, respectively, with little dependency over the observed heliocentric distances of R=1.0$-$2.3au. For Phaethon, e…
The near-Earth objects (NEOs) (3200) Phaethon and (155140) 2005 UD are thought to share a common origin, with the former exhibiting dust activity at perihelion that is thought to directly supply the Geminid meteor stream. Both of these objects currently have very small perihelion distances, which results in them having perihelion temperatures of or exceeding 1000 K. The current activity from Phaethon is relevant to the destruction of NEOs close to the Sun, which most likely has produced meteor streams linked to asteroids in the past. We model the past thermal characteristics of Phaethon and 20…
Accurate estimation of brightness of (3200) Phaethon up to lower phase angles are essential for planning of the on-board camera of the DESTINY$^{+}$ mission. We have carried out intensive observations of Phaethon in the optical wavelength ($g$, $r$, and $i$) with the TriCCS camera on the Seimei 3.8 m telescope in October and November, 2021. We derived the absolute magnitude $H_\mathrm{V}$ and the slope parameter $G$ of Phaethon as $H_\mathrm{V}=14.23\pm0.02$ and $G=0.040\pm0.008$ from multiple photometric observations including lower phase angles down to $\sim$9$^{\circ}$ with the $H$-$G$ mode…
The JAXA/ISAS spacecraft DESTINY$^+$ will be launched to the active asteroid (3200) Phaethon in 2022. Among the proposed core payload is the DESTINY+ Dust Analyzer (DDA) which is an upgrade of the Cosmic Dust Analyzer flown on the Cassini spacecraft to Saturn (Srama et al. 2011). We use two up-to-date computer models, the ESA Interplanetary Meteoroid Engineering Model (IMEM, Dikarev et al. 2005), and the interstellar dust module of the Interplanetary Meteoroid environment for EXploration model (IMEX; Sterken2013 et al., Strub et al. 2019) to study the detection conditions and fluences of inter…
The linear polarization degree (referred to the scattering plane, P_r) as a function of the solar phase angle, α, of solar system objects is a good diagnostic to understand the scattering properties of their surface materials. We report Pr of Phaethon over a wide range of α from 19.1 deg to 114.3 deg in order to better understanding properties of its surface materials. The derived phase-polarization curve shows that the maximum of P_r, P_max, is >42.4% at α >114.3 deg, a value significantly larger than those of the moderate albedo asteroids (P_max ~9%). The phase-polarization curve classifies …
Time-series multi-band photometry and spectrometry were performed in Nov.-Dec. 2017 to investigate the homogeneity of the surface of asteroid (3200) Phaethon. We found that Phaethon is a B-type asteroid, in agreement with previous studies, and that it shows no evidence for rotational color variation. The sub-solar latitude during our observation period was approximately 55 degree S, which corresponded to the southern hemisphere of Phaethon. Thus, we found that the southern hemisphere of Phaethon has a homogeneous surface. We compared our spectra with existing spectral data to examine the latit…
The near-Earth asteroid (3200) Phaethon is an intriguing object: its perihelion is at only 0.14 au and is associated with the Geminid meteor stream. We aim to use all available disk-integrated optical data to derive a reliable convex shape model of Phaethon. By interpreting the available space- and ground-based thermal infrared data and Spitzer spectra using a thermophysical model, we also aim to further constrain its size, thermal inertia, and visible geometric albedo. We applied the convex inversion method to the new optical data obtained by six instruments and to previous observations. The …
We report on the first polarimetric study of (3200) Phaethon, the target of JAXA's DESTINY$^+$ mission, in the negative branch to ensure its anhydrous nature and to derive an accurate geometric albedo. We conducted observations at low phase angles (Sun-target-observer angle, alpha = 8.8-32.4 deg) from 2021 October to 2022 January and found that Phaethon has a minimum polarization degree $P_{min}$ = -1.3 +- 0.1 %, a polarimetric slope h = 0.22 +- 0.02 % deg$^{-1}$, and an inversion angle alpha$_0$ = 19.9 +- 0.3 deg. The derived geometric albedo is $p_V$ = 0.11 (in the range of 0.08-0.13). These…
The recent close approach of the NEA (3200) Phaethon offered a rare opportunity to obtain high-quality observational data. We used the newly obtained optical light curves to improve the spin and shape model of Phaethon and to determine its surface physical properties derived by thermophysical modeling. We also used the available astrometric observations of Phaethon, including those obtained by the Arecibo radar and the Gaia spacecraft, to constrain the secular drift of the orbital semimajor axis. This constraint allowed us to estimate the bulk density by assuming that the drift is dominated by…
We report on optical polarimetric observations of two Apollo type near-Earth asteroids, (422699) 2000 PD3 and (3200) Phaethon, and BVRI photometric observations of 2000 PD3 using the 1.6m Pirka telescope in 2017. We derived the geometric albedo of pv = 0.22 +- 0.06 and the color indices (B-V = 0.282 +- 0.072, V-R = 0.198 +- 0.035 and V-I = 0.203 +- 0.022) for 2000 PD3 which are consistent with those of S-type asteroids (including Q-types). The effective diameter of 2000 PD3 was derived as 0.69 +- 0.15 km using our derived geometric albedo. We found that our polarimetric data of Phaethon in 201…
Solar system bodies with surface and sub-surface volatiles will show observational evidence of activity when they reach a temperature where those volatiles change from solid to gas and are released. This is most frequently seen in comets, where activity is driven by the sublimation of water, carbon dioxide, or carbon monoxide ices. However, some bodies (notably the asteroid (3200) Phaethon) show initiation of activity at very small heliocentric distances, long after they have reached the sublimation temperatures of these ices. We investigate whether the sodium present in the mineral matrix cou…
In 2010 Jewitt and Li published a paper examining the behavior of comet-asteroid transition object 3200 Phaethon, arguing it was asteroid-like in its behavior throughout most of its orbit, but that near its perihelion, at a distance of only 0.165 AU from the sun, its dayside temperatures would be hot enough to vaporize rock (>1000 K, Hanus et al. 2016). Thus it would act like a "rock comet" as gases produced from evaporating rock were released from the body, in a manner similar to the more familiar sublimation of water ice into vacuum seen for comets coming within ~3 AU of the Sun. In this Not…
Thermophysical models allow for improved constraints on the physical and thermal surface properties of asteroids beyond what can be inferred from more simple thermal modeling, provided a sufficient number of observations is available. We present thermophysical modeling results of observations from the NEOWISE mission for two near-Earth asteroids which are the targets of the DESTINY+ flyby mission: (3200) Phaethon and (155140) 2005 UD. Our model assumes a rotating, cratered, spherical surface, and employs a Monte Carlo Markov Chain to explore the multi-dimensional parameter space of the fit. We…
The recently discovered near-Earth asteroid 2021 PH27 has the shortest orbital period of all known asteroids. It cannot be excluded that 2021 PH27 is also an active asteroid, as (3200) Phaethon. We intend to estimate the consequences of this hypothesis, although testing is difficult with ground-based observations during perihelion passages, due to low solar elongation. Assuming a surface activity similar to that of Phaethon, an increase in brightness of about 1.4 mag can be estimated. Since it is an asteroid with a MOID of $0.014660 \pm 0.000034$ AU with Venus, 2021 PH27 could be the equivalen…
We present an analysis of asteroid (3200) Phaethon using coronagraphic observations from 2008 to 2022 by the COR2 cameras onboard the twin Solar TErrestrial RElations Observatory (STEREO) spacecraft. Although undetected in individual images, Phaethon was visible in stacks combined from the same perihelion observations, yet only at small ($\lesssim$30°) but not large ($\gtrsim$150°) phase angles. The observations are in line with the contribution from a bare nucleus, thereby seriously contradicting the interpretation based on HI-1 observations that attributes the perihelion activity to the ejec…
Asteroid (16) Psyche, that for long was the largest M-type with no detection of hydration features in its spectrum, was recently discovered to have a weak 3 micron band and thus it eventually was added to the group of hydrated asteroids. Its relatively high density in combination with the high radar albedo, led to classify the asteroid as a metallic object, possibly a core of a differentiated body, remnant of "hit-and-run" collisions. The detection of hydration is, in principle, inconsistent with a pure metallic origin of this body. Here we consider the scenario that the hydration on its surfa…
DESTINY+ is an upcoming JAXA Epsilon medium-class mission to fly by the Geminids meteor shower parent body (3200) Phaethon. It will be the world's first spacecraft to escape from a near-geostationary transfer orbit into deep space using a low-thrust propulsion system. In doing so, DESTINY+ will demonstrate a number of technologies that include a highly efficient ion engine system, lightweight solar array panels, and advanced asteroid flyby observation instruments. These demonstrations will pave the way for JAXA's envisioned low-cost, high-frequency space exploration plans. Following the Phaeth…
Context. Recent observations of dust ejections from active asteroids, including (3200) Phaethon, have drawn considerable interest from planetary astronomers studying the generation and removal of small dust particles on asteroids. Aims. In this work, we aim to investigate the importance of thermal radiation pressure from asteroid regolith (AR) acting on small dust particles over the surface of the AR. In particular, we aim to understand the role of thermal radiation in the near-Sun environment. Methods. We describe the acceleration of particles over the AR within the radiation fields (direct s…
The investigation of asteroids near the Sun is important for understanding the final evolutionary stage of primitive solar system objects. A near-Sun asteroid, (155140) 2005 UD, has orbital elements similar to those of (3200) Phaethon (the target asteroid for the JAXA's $DESTINY^+$ mission). We conducted photometric and polarimetric observations of 2005 UD and found that this asteroid exhibits a polarization phase curve similar to that of Phaethon over a wide range of observed solar phase angles ($ α= 20 - 105^\circ $) but different from those of (101955) Bennu and (162173) Ryugu (asteroids co…
We present thermal infrared observations of the active asteroid (and Geminid meteoroid stream parent) 3200 Phaethon using the Very Large Telescope. The images, at 10.7 micron wavelength, were taken with Phaethon at its closest approach to Earth (separation 0.07 AU) in 2017 December, at a linear resolution of about 14 km. We probe the Hill sphere (of radius 66 km) for trapped dust and macroscopic bodies, finding neither, and we set limits to the presence of unbound dust. The derived limits to the optical depth of dust near Phaethon depend somewhat on the assumed geometry, but are of order 1e-5.…
We present Hubble Space Telescope observations of the active asteroid (and Geminid stream parent) 3200 Phaethon when at its closest approach to Earth (separation 0.07 AU) in 2017 December. Images were recorded within $\sim$1\degr~of the orbital plane, providing extra sensitivity to low surface brightness caused by scattering from a large-particle trail. We placed an upper limit to the apparent surface brightness of such a trail at 27.2 magnitudes arcsecond$^{-2}$, corresponding to an in-plane optical depth $\le 3\times10^{-9}$. No co-moving sources brighter than absolute magnitude 26.3, corres…
(3200) Phaethon is a compelling object as it has an asteroidal appearance and spectrum, produces a weak dust tail during perihelion at just 0.14 AU, and is the parent body of the Geminid Meteor Shower. A better understanding of the physical properties of Phaethon is needed to understand the nature of its current and previous activity, relationship to potential source populations, and to plan for the upcoming flyby of the DESTINY+ spacecraft of Phaethon in the 2020s. We performed rotationally-resolved spectroscopy of Phaethon at visible and near-infrared wavelengths (0.4-2.5 microns) in 2007 an…
We present a deep imaging and spectroscopic search for emission from (3200) Phaethon, a large near-Earth asteroid that appears to be the parent of the strong Geminid meteoroid stream, using the 4.3 m Lowell Discovery Telescope. Observations were conducted on 2017 December 14-18 when Phaethon passed only 0.07 au from the Earth. We determine the $3σ$ upper level of dust and CN production rates to be 0.007-0.2 $\mathrm{kg~s^{-1}}$ and $2.3\times10^{22}~\mathrm{molecule~s^{-1}}$ through narrowband imaging. A search in broadband images taken through the SDSS $r'$ filter shows no 100-m-class fragmen…
We present an update to the first white-light detections of a dust trail observed closely following the orbit of asteroid (3200) Phaethon, as seen by the Wide-field Imager for Parker Solar Probe (WISPR) instrument on the NASA Parker Solar Probe (PSP) mission. Here we provide a summary and analysis of observations of the dust trail over nine separate mission encounters between October 2018 and August 2021 that saw the spacecraft approach to within 0.0277 au of the orbit of Phaethon. We find the photometric and estimated dust mass properties to be inline with those in the initial publication, wi…
Here we report a comparison between reflectance spectroscopy of meteorites under asteroidal environment (high vacuum and temperature) and Main Belt and Near Earth Asteroids spectra. Focusing on the OH absorption feature around 3μm, we show that the asteroidal environment induces a reduction of depth and width of the band, as well as a shift of the reflectance minimum. We then decompose the OH feature into several components with a new model using Exponentially Modified Gaussians. Unlike previous studies, we confirme the link between these components, the aqueous alteration history and the amou…
In order to search for evidence of hydration on M-type asteroid (16) Psyche, we observed this object in the 3 micron spectral region using the long-wavelength cross-dispersed (LXD: 1.9-4.2 micron) mode of the SpeX spectrograph/imager at the NASA Infrared Telescope Facility (IRTF). Our observations show that Psyche exhibits a 3 micron absorption feature, attributed to water or hydroxyl. The 3 micron absorption feature is consistent with the hydration features found on the surfaces of water-rich asteroids, attributed to OH- and/or H2O-bearing phases (phyllosilicates). The detection of a 3 micron…
Apollo-type NEA (3200) Phaethon, classified at the B/F-type taxonomy, probably the main mass of the Phaethon-Geminid stream complex (PGC), can be the most metamorphic C-complex asteroid in our solar system, since it is heated up to ~1000 K by the solar radiation around its perihelion passages. Hence, its surface material may be easily decomposed in near-sun environment. Phaethon's spectrum exhibits extremely blue-slope in the VIS-NIR region (so-called Phaethon Blue). Another candidate large member of the PGC, (155140) 2005 UD, shows a B/F-type color, however with a C-type-like red color over i…
Comets can exhibit non-gravitational accelerations caused by recoil forces due to anisotropic mass loss. So might active asteroids. We present an astrometric investigation of 18 active asteroids in search of non-gravitational acceleration. Statistically significant (signal-to-noise ratio (SNR) $> 3$) detections are obtained in three objects: 313P/Gibbs, 324P/La Sagra and (3200) Phaethon. The strongest and most convincing detection ($>$7$σ$ in each of three orthogonal components of the acceleration), is for the $\sim$1 km diameter nucleus of 324P/La Sagra. A 4.5$σ$ detection of the transverse c…
We present here a new method to model the shape of the 3-μm absorption band in the reflectance spectra of meteorites and small bodies. The band is decomposed into several OH/H2O components using Exponentially Modified Gaussian (EMG) profiles, as well as possible organic components using Gaussian profiles when present. We compare this model to polynomial and multiple Gaussian profile fits and show that the EMGs model returns the best rendering of the shape of the band, with significantly lower residuals. We also propose as an example an algorithm to estimate the error on the band parameters usi…
Fast Rotation of a Sub-km-sized Near-Earth Object 2011 XA3
我们介绍了近地天体（NEO）2011 XA 3的光变曲线观测及其多波段测光。光变曲线的周期为0.0304 ± 0.0003天（= 43.8 ± 0.4分钟）。快速旋转表明2011 XA 3处于张力状态（即整体小行星），无法通过自引力保持在一起。多波段光度分析表明2011 XA 3的分类类别为S-复合体或V-型。其有效直径分别为225 ± 97 m（S-复合体）和166 ± 63 m（V-型）。因此，2011 XA 3是第二大快速旋转单体小行星的候选者。此外，2011 XA 3的轨道参数与近地天体（3200）法厄同的轨道参数相似，但属于F/B型。我们计算了2011年XA 3和Phaethon的轨道演化。然而，计算结果和不同的分类表明，这两颗小行星都不是共同的起源。
The near-Earth asteroid 3200 Phaethon (1983 TB) is an attractive object not only from a scientific viewpoint but also because of JAXA's DESTINY+ target. The rotational lightcurve and spin properties were investigated based on the data obtained in the ground-based observation campaign of Phaethon. We aim to refine the lightcurves and shape model of Phaethon using all available lightcurve datasets obtained via optical observation, as well as our time-series observation data from the 2017 apparition. Using eight 1-2-m telescopes and an optical imager, we acquired the optical lightcurves and deriv…
Here were report on a laboratory study aiming to reproduce specificities of near-Earth Asteroid. We study how the elevated surface temperature, their surface roughness (rock or regolith), as well as observation geometry can affect the absorption features detected on asteroids. For that purpose, we selected a recent carbonaceous chondrite fall, the Mukundpura CM2 chondrite which fell in India in June 2017. Bidirectional reflectance spectroscopy was performed to analyze the effect of the geometrical configuration (incidence, emergence and azimuth angle) on the measurement. Our results show that …
We conducted a polarimetric observation of the fast-rotating near-Earth asteroid (1566) Icarus at large phase (Sun-asteroid-observer's) angles $α$= 57 deg--141deg around the 2015 summer solstice. We found that the maximum values of the linear polarization degree are $P_\mathrm{max}$=7.32$\pm$0.25 % at phase angles of $α_\mathrm{max}$=124$\pm$8 deg in the $V$-band and $P_\mathrm{max}$=7.04$\pm$0.21 % at $α_\mathrm{max}$=124$\pm$6 deg in the $R_\mathrm{C}$-band. Applying the polarimetric slope-albedo empirical law, we derived a geometric albedo of $p_\mathrm{V}$=0.25$\pm$0.02, which is in agreem…
