The near-Earth asteroid (99942) Apophis is a potentially hazardous asteroid. We obtained far-infrared observations of this asteroid with the Herschel Space Observatory PACS instrument at 70, 100, and ...160 μm. These were taken at two epochs in January and March 2013 during a close-Earth encounter. These first thermal measurements of Apophis were taken at similar phase angles before and after opposition. We performed a detailed thermophysical model analysis by using the spin and shape model recently derived from applying a two-period Fourier series method to a large sample of well-calibrated photometric observations. We found that the tumbling asteroid Apophis has an elongated shape with a mean diameter of 375+14-10 m (of an equal volume sphere) and a geometric V-band albedo of 0.30+0.05-0.06. We found a thermal inertia in the range 250–800 Jm-2 s-0.5 K-1 (best solution at Γ = 600 Jm-2 s-0.5 K-1), which can be explained by a mixture of low-conductivity fine regolith with larger rocks and boulders of high thermal inertia on the surface. The thermal inertia, and other similarities with (25143) Itokawa indicate that Apophis might also have a rubble-pile structure. If we combine the new size value with the assumption of an Itokawa-like density and porosity we estimate a mass between 4.4 and 6.2 × 1010 kg, which is more than 2–3 times larger than previous estimates. We expect that the newly derived properties will influence impact scenario studies and the long-term orbit predictions of Apophis.
Context.
Thanks to the
Gaia
mission, it will be possible to determine the masses of approximately hundreds of large main belt asteroids with very good precision. We currently have diameter estimates ...for all of them that can be used to compute their volume and hence their density. However, some of those diameters are still based on simple thermal models, which can occasionally lead to volume uncertainties as high as 20–30%.
Aims.
The aim of this paper is to determine the 3D shape models and compute the volumes for 13 main belt asteroids that were selected from those targets for which
Gaia
will provide the mass with an accuracy of better than 10%.
Methods.
We used the genetic Shaping Asteroids with Genetic Evolution (SAGE) algorithm to fit disk-integrated, dense photometric lightcurves and obtain detailed asteroid shape models. These models were scaled by fitting them to available stellar occultation and/or thermal infrared observations.
Results.
We determine the spin and shape models for 13 main belt asteroids using the SAGE algorithm. Occultation fitting enables us to confirm main shape features and the spin state, while thermophysical modeling leads to more precise diameters as well as estimates of thermal inertia values.
Conclusions.
We calculated the volume of our sample of main-belt asteroids for which the
Gaia
satellite will provide precise mass determinations. From our volumes, it will then be possible to more accurately compute the bulk density, which is a fundamental physical property needed to understand the formation and evolution processes of small Solar System bodies.
Despite the growing importance of planetary Space Weather forecasting and radiation protection for science and robotic exploration and the need for accurate Space Weather monitoring and predictions, ...only a limited number of spacecraft have dedicated instrumentation for this purpose. However, every spacecraft (planetary or astronomical) has hundreds of housekeeping sensors distributed across the spacecraft, some of which can be useful to detect radiation hazards produced by solar particle events. In particular, energetic particles that impact detectors and subsystems on a spacecraft can be identified by certain housekeeping sensors, such as the Error Detection and Correction (EDAC) memory counters, and their effects can be assessed. These counters typically have a sudden large increase in a short time in their error counts that generally match the arrival of energetic particles to the spacecraft. We investigate these engineering datasets for scientific purposes and perform a feasibility study of solar energetic particle event detections using EDAC counters from seven European Space Agency Solar System missions: Venus Express, Mars Express, ExoMars‐Trace Gas Orbiter, Rosetta, BepiColombo, Solar Orbiter, and Gaia. Six cases studies, in which the same event was observed by different missions at different locations in the inner Solar System are analyzed. The results of this study show how engineering sensors, for example, EDAC counters, can be used to infer information about the solar particle environment at each spacecraft location. Therefore, we demonstrate the potential of the various EDAC to provide a network of solar particle detections at locations where no scientific observations of this kind are available.
Plain Language Summary
Space Weather is the discipline that aims at understanding and predicting the state of the Sun, interplanetary medium and its impact on planetary environments. One source of Space Weather is Solar Energetic Particles (SEPs), which are emitted by the Sun and enhance the radiation and particles that flow in space. Predicting the motion of these particles is important but difficult as we need good satellite coverage of the entire inner Solar System, and only a limited number of spacecraft have the necessary instrumentation. Thanks to the European Space Agency flotilla, that is, Venus Express, Mars Express, ExoMars‐Trace Gas Orbiter, Rosetta, BepiColombo, Solar Orbiter, and Gaia, we performed a feasibility study of the detection of SEP events using engineering sensors in the main body of the spacecraft that were originally placed there to monitor its health during the mission. We explored how much scientific information we can get from these engineering sensors, such as the timing and duration of an SEP impacting the spacecraft, or the minimum energy of those particles to trigger a detection. The results of this study have the potential of providing a good network of solar particle detections at locations where no scientific observations are available.
Key Points
Space weather detections using housekeeping datasets on European Space Agency spacecraft
Some engineering datasets on spacecraft have the potential to be used for science
Same Space Weather events detected with housekeeping data at widely‐spaced locations in the Solar System
We present initial results from the Herschel GT key program: Herschel observations of EXtra-Ordinary Sources (HEXOS) and outline the promise and potential of spectral surveys with Herschel/HIFI. The ...HIFI instrument offers unprecedented sensitivity, as well as continuous spectral coverage across the gaps imposed by the atmosphere, opening up a largely unexplored wavelength regime to high-resolution spectroscopy. We show the spectrum of Orion KL between 480 and 560 GHz and from 1.06 to 1.115 THz. From these data, we confirm that HIFI separately measures the dust continuum and spectrally resolves emission lines in Orion KL. Based on this capability we demonstrate that the line contribution to the broad-band continuum in this molecule-rich source is ~20–40% below 1 THz and declines to a few percent at higher frequencies. We also tentatively identify multiple transitions of HD18O in the spectra. The first detection of this rare isotopologue in the interstellar medium suggests that HDO emission is optically thick in the Orion hot core with HDO/H2O ~ 0.02. We discuss the implications of this detection for the water D/H ratio in hot cores.
Aims. We seek to constrain the surface composition of the trans-Neptunian object (90482) Orcus and its small satellite Vanth, as well as their mass and density. Methods. We acquired near-infrared ...spectra (1.4−2.4 μm) of (90482) Orcus and its companion Vanth using the adaptive-optics-fed integral-field spectrograph SINFONI mounted on Yepun/UT4 at the European Southern Observatory Very Large Telescope. We took advantage of a very favorable appulse (separation of only 4″) between Orcus and the UCAC2 29643541 star (mR = 11.6) to use the adaptive optics mode of SINFONI, allowing both components to be spatially resolved and Vanth colors to be extracted independently from Orcus. Results. The spectrum of Orcus we obtain has the highest signal-to-noise ratio to date, and we confirm the presence of H2O ice in crystalline form, together with the presence of an absorption band at 2.2 μm. We set an upper limit of about 2% to the presence of methane, and 5% for ethane. Since the methane alone cannot account for the 2.2 μm band, the presence of ammonia is suggested to the level of a couple of percent. The colors of Vanth are found to be slightly redder than those of Orcus, but the large measurement uncertainties prevent us from drawing any firm conclusions about the origin of the pair (capture or co-formation). Finally, we reset the orbital phase of Vanth around Orcus, and confirm the orbital parameters derived by Brown and collaborators.
We present here a comparison of our results from ground-based observations of asteroid (21) Lutetia with imaging data acquired during the flyby of the asteroid by the ESA Rosetta mission. This flyby ...provided a unique opportunity to evaluate and calibrate our method of determination of size, 3-D shape, and spin of an asteroid from ground-based observations. Knowledge of certain observable physical properties of small bodies (e.g., size, spin, 3-D shape, and density) have far-reaching implications in furthering our understanding of these objects, such as composition, internal structure, and the effects of non-gravitational forces. We review the different observing techniques used to determine the above physical properties of asteroids and present our 3-D shape-modeling technique KOALA – Knitted Occultation, Adaptive-optics, and Lightcurve Analysis – which is based on multi-dataset inversion. We compare the results we obtained with KOALA, prior to the flyby, on asteroid (21) Lutetia with the high-spatial resolution images of the asteroid taken with the OSIRIS camera on-board the ESA Rosetta spacecraft, during its encounter with Lutetia on 2010 July 10. The spin axis determined with KOALA was found to be accurate to within 2°, while the KOALA diameter determinations were within 2% of the Rosetta-derived values. The 3-D shape of the KOALA model is also confirmed by the spectacular visual agreement between both 3-D shape models (KOALA pre- and OSIRIS post-flyby). We found a typical deviation of only 2km at local scales between the profiles from KOALA predictions and OSIRIS images, resulting in a volume uncertainty provided by KOALA better than 10%. Radiometric techniques for the interpretation of thermal infrared data also benefit greatly from the KOALA shape model: the absolute size and geometric albedo can be derived with high accuracy, and thermal properties, for example the thermal inertia, can be determined unambiguously. The corresponding Lutetia analysis leads to a geometric albedo of 0.19±0.01 and a thermal inertia below 40Jm−2s−0.5K−1, both in excellent agreement with the Rosetta findings. We consider this to be a validation of the KOALA method. Because space exploration will remain limited to only a few objects, KOALA stands as a powerful technique to study a much larger set of small bodies using Earth-based observations.
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We present Herschel/HIFI observations of the fundamental rotational transitions of ortho- and para-H216O and H218O in absorption towards Sagittarius B2(M) and W31C. The ortho/para ratio in water in ...the foreground clouds on the line of sight towards these bright continuum sources is generally consistent with the statistical high-temperature ratio of 3, within the observational uncertainties. However, somewhat unexpectedly, we derive a low ortho/para ratio of 2.35 +/- 0.35, corresponding to a spin temperature of similar to 27 K, towards Sagittarius B2(M) at velocities of the expanding molecular ring. Water molecules in this region appear to have formed with, or relaxed to, an ortho/para ratio close to the value corresponding to the local temperature of the gas and dust.
Macronutrients, comprising carbohydrates, proteins and lipids, underpin many ecological processes, but their quantification in ecological studies is often inaccurate and laborious, requiring large ...investments of time and bulk samples, which make individual‐level studies impossible. This study presents Macronutrient Extraction and Determination from Invertebrates (MEDI), a protocol for the direct, rapid and relatively low‐cost determination of macronutrient content from single small macroinvertebrates.
Macronutrients were extracted by a sequential process of soaking in 1:12 chloroform:methanol solution to remove lipid and then solubilising tissue in 0.1 M NaOH. Proteins, carbohydrates and lipids were determined by colorimetric assays from the same individual specimens.
The limits of detection of MEDI with the equipment and conditions used were 0.067, 0.065 and 0.006 mg/ml for proteins, carbohydrates and lipids respectively. Adjusting the volume of reagents used for extraction and determination can broaden the range of concentrations that can be detected. MEDI successfully identified taxonomic differences in macronutrient content between five insect species.
Macronutrient Extraction and Determination from Invertebrates can directly and rapidly determine macronutrient content in tiny (dry mass ~3 mg) and much larger individual invertebrates. Using MEDI, the total macronutrient content of over 50 macroinvertebrates can be determined within around 3 days of collection at a cost of ~$1.35 per sample.
Mae macromaetholion, sy'n cynnwys carbohydradau, proteinau a lipidau, yn sail i lawer o brosesau ecolegol, ond mae eu meintioli mewn astudiaethau yn aml yn medru bod yn wallus ac yn llafurus, ac yn galw am fuddsoddiadau mawr mewn amser a swmp‐samplau. Gwna hyn astudiaethau ar lefel unigol yn amhosibl. Mae'r astudiaeth hon yn disgrifio MEDI (Echdyniad ac Adnabod Macromaetholion o Anifeiliaid Di‐asgwrn‐cefn), protocol newydd sy'n mesur ac adnabod macromaetholion yn uniongyrchol, ond yn gyflym ac yn gymharol rad, o facroinfertebratau bach sengl.
Echdynnwyd macromaetholion trwy glain‐guriad mewn hydoddiant clorofform 1:12 methanol i waredu'r lipid, cyn hydoddi'r meinwe mewn 0.1M NaOH. Adnabuwyd proteinau, carbohydradau a lipidau gan brofion lliwmetrig o'r un sbesimenau.
Cyfyngiadau darganfod MEDI gyda'r offer a ddefnyddiwyd oedd 0.067, 0.065 a 0.006 mg/ml ar gyfer proteinau, carbohydradau a lipidau, yn ôl eu trefn. Gall addasu cryfderau'r adweithyddion a ddefnyddir i echdynnu ac adnabod ehangu'r ystod o grynodiadau y gellir eu canfod. Llwyddodd MEDI i nodi gwahaniaethau tacsonomig mewn cynnwys macrofaetholion rhwng pum rhywogaeth o bryfed.
Gall MEDI bennu cynnwys macromaetholion yn gywir, yn uniongyrchol ac yn gyflym, mewn anifeiliaid di‐asgwrn cefn bach (màs sych ~3 mg) a mawr. Gan ddefnyddio MEDI, gellir pennu cyfanswm cynnwys dros 50 o facromaetholion o fewn oddeutu tridiau am gost o tua $ 1.35 y sampl.
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