共查询到20条相似文献，搜索用时 93 毫秒
1.
Lisse CM Christian DJ Dennerl K Meech KJ Petre R Weaver HA Wolk SJ 《Science (New York, N.Y.)》2001,292(5520):1343-1348
Using soft x-ray observations of the bright new comet C/1999 S4 (LINEAR) with the Chandra x-ray observatory, we have detected x-ray line emission created by charge exchange between highly ionized solar wind minor ions and neutral gases in the comet's coma. The emission morphology was symmetrically crescent shaped and extended out to 300,000 kilometers from the nucleus. The emission spectrum contains 6 lines at 320, 400, 490, 560, 600, and 670 electron volts, attributable to electron capture and radiative deexcitation by the solar wind species C(+5), C(+6), N(+7), O(+7), and O(+8). A contemporaneous 7-day soft x-ray light curve obtained using the Extreme Ultraviolet Explorer demonstrates a large increase in the comet's emission coincident with a strong solar flare on 14 and 15 July 2000. 相似文献
2.
Beiersdorfer P Boyce KR Brown GV Chen H Kahn SM Kelley RL May M Olson RE Porter FS Stahle CK Tillotson WA 《Science (New York, N.Y.)》2003,300(5625):1558-1559
In laboratory experiments using the engineering spare microcalorimeter detector from the ASTRO-E satellite mission, we recorded the x-ray emission of highly charged ions of carbon, nitrogen, and oxygen, which simulates charge exchange reactions between heavy ions in the solar wind and neutral gases in cometary comae. The spectra are complex and do not readily match predictions. We developed a charge exchange emission model that successfully reproduces the soft x-ray spectrum of comet Linear C/1999 S4, observed with the Chandra X-ray Observatory. 相似文献
3.
High-resolution images of the sun in the soft x-ray to extreme ultraviolet(EUV) regime have been obtained with normal-incidence Cassegrain multilayer telescopes operated from a sounding rocket in space. The inherent energy-selective property of multilayer-coated optics allowed distinct groups of emission lines to be isolated in the solar corona and the transition region. The Cassegrain telescopes provided images in bands centered at 173 and 256 angstroms. The bandpass centered at 173 angstroms is dominated by emission from the ions Fe IX Fe X. This emission is from coronal plasma in the temperature range 0.8 x 10(6) to 1.4 x 10(6)K. The images have angular resolution of about 1.0 to 1.5 arc seconds, and show no degradation because of x-ray scattering. Many features of coronal structure, including magnetically confined loops of hot plasma, coronal plumes, polar coronal holes, faint structures on the size scale of supergranulation and smaller, and features due to overlying cool prominences are visible in the images. The density structure of polar plumes, which are thought to contribute to the solar wind, has been derived from the observations out to 1.7 solar radii. 相似文献
4.
Fink U 《Science (New York, N.Y.)》1992,257(5078):1926-1929
As part of a program to determine the chemical composition of a sample population of comets, a very unusual comet, Yanaka (1988r), was observed in January 1989. Although the comet showed the usual emissions of Ol and NH(2), it did not display any hint of C(2) or CN emission. The comet is depleted in C(2) by at least a factor of 100 and in CN by a factor of 25 relative to typical comets. If comets originate from interstellar clouds, Yanaka (1988r) could be an interloper from a cloud of different composition. If Yanaka (1988r) was formed within our solar system, the solar nebula was less uniform than assumed by most present models of formation. 相似文献
5.
Hogerheijde MR Bergin EA Brinch C Cleeves LI Fogel JK Blake GA Dominik C Lis DC Melnick G Neufeld D Panić O Pearson JC Kristensen L Yildiz UA van Dishoeck EF 《Science (New York, N.Y.)》2011,334(6054):338-340
Icy bodies may have delivered the oceans to the early Earth, yet little is known about water in the ice-dominated regions of extrasolar planet-forming disks. The Heterodyne Instrument for the Far-Infrared on board the Herschel Space Observatory has detected emission lines from both spin isomers of cold water vapor from the disk around the young star TW Hydrae. This water vapor likely originates from ice-coated solids near the disk surface, hinting at a water ice reservoir equivalent to several thousand Earth oceans in mass. The water's ortho-to-para ratio falls well below that of solar system comets, suggesting that comets contain heterogeneous ice mixtures collected across the entire solar nebula during the early stages of planetary birth. 相似文献
6.
Photometry and spectroscopy of the object Cha Halpha 1, located in the Chamaeleon I star-forming cloud, show that it is a approximately 10(6)-year-old brown dwarf with spectral type M7.5 to M8 and 0.04 +/- 0.01 solar masses. Quiescent x-ray emission was detected in a 36-kilosecond observation with 31.4 +/- 7.7 x-ray photons, obtained with the Rontgen Satellite (ROSAT), with 9final sigma detection significance. This corresponds to an x-ray luminosity of 2.57 x 10(28) ergs per second and an x-ray to bolometric luminosity ratio of 10(-3.44). These are typical values for late M-type stars. Because the interior of brown dwarfs may be similar to that of convective late-type stars, which are well-known x-ray sources, x-ray emission from brown dwarfs may indicate magnetic activity. 相似文献
7.
Levison HF Morbidelli A Dones L Jedicke R Wiegert PA Bottke WF 《Science (New York, N.Y.)》2002,296(5576):2212-2215
We have calculated the number of dormant, nearly isotropic Oort cloud comets in the solar system by (i) combining orbital distribution models with statistical models of dormant comet discoveries by well-defined surveys and (ii) comparing the model results to observations of a population of dormant comets. Dynamical models that assume that comets are not destroyed predict that we should have discovered approximately 100 times more dormant nearly isotropic comets than are actually seen. Thus, as comets evolve inward from the Oort cloud, the majority of them must physically disrupt. 相似文献
8.
A new technique has made it possible to measure the velocity of portions of the solar wind during its flow outward from the sun. This analysis utilizes spacecraft (ISEE-3) observations of radio emission generated in regions of the solar wind associated with solar active regions. By tracking the source of these radio waves over periods of days, it is possible to measure the motion of the emission regions. Evidence of solar wind acceleration during this outward flow, consistent with theoretical models, has also been obtained. 相似文献
9.
Caraveo PA Bignami GF DeLuca A Mereghetti S Pellizzoni A Mignani R Tur A Becker W 《Science (New York, N.Y.)》2003,301(5638):1345-1347
We report the X-ray Multimirror Mission-Newton European Photon Imaging Camera observation of two elongated parallel x-ray tails trailing the pulsar Geminga. They are aligned with the object's supersonic motion, extend for approximately 2', and have a nonthermal spectrum produced by electron-synchrotron emission in the bow shock between the pulsar wind and the surrounding medium. Electron lifetime against synchrotron cooling matches the source transit time over the x-ray features' length. Such an x-ray detection of a pulsar bow shock (with no Halpha emission) allows us to gauge the pulsar electron injection energy and the shock magnetic field while constraining the angle of Geminga's motion and the local matter density. 相似文献
10.
Cirtain JW Golub L Lundquist L van Ballegooijen A Savcheva A Shimojo M Deluca E Tsuneta S Sakao T Reeves K Weber M Kano R Narukage N Shibasaki K 《Science (New York, N.Y.)》2007,318(5856):1580-1582
Coronal magnetic fields are dynamic, and field lines may misalign, reassemble, and release energy by means of magnetic reconnection. Giant releases may generate solar flares and coronal mass ejections and, on a smaller scale, produce x-ray jets. Hinode observations of polar coronal holes reveal that x-ray jets have two distinct velocities: one near the Alfvén speed ( approximately 800 kilometers per second) and another near the sound speed (200 kilometers per second). Many more jets were seen than have been reported previously; we detected an average of 10 events per hour up to these speeds, whereas previous observations documented only a handful per day with lower average speeds of 200 kilometers per second. The x-ray jets are about 2 x 10(3) to 2 x 10(4) kilometers wide and 1 x 10(5) kilometers long and last from 100 to 2500 seconds. The large number of events, coupled with the high velocities of the apparent outflows, indicates that the jets may contribute to the high-speed solar wind. 相似文献
11.
Vaiana GS Reidy WP Zehnpfennig T Vanspeybroeck L Giacconi R 《Science (New York, N.Y.)》1968,161(3841):564-567
High-resolution solar x-ray images were obtained with a rocket-borne grazing incidence telescope. The x-ray flare is large in extent, has fine strulctuire, and follows a neutral magnetic line. X-ray emitting coronal links interconnect active regions. The general coronal emission at the limb and several faint regions on the disc are observed. 相似文献
12.
Stappers BW Gaensler BM Kaspi VM van der Klis M Lewin WH 《Science (New York, N.Y.)》2003,299(5611):1372-1374
We have detected an x-ray nebula around the binary millisecond pulsar B1957+20. A narrow tail, corresponding to the shocked pulsar wind, is seen interior to the known Halpha bow shock and proves the long-held assumption that the rotational energy of millisecond pulsars is dissipated through relativistic winds. Unresolved x-ray emission likely represents the shock where the winds of the pulsar and its companion collide. This emission indicates that the efficiency with which relativistic particles are accelerated in the postshock flow is similar to that for young pulsars, despite the shock proximity and much weaker surface magnetic field of this millisecond pulsar. 相似文献
13.
Mumma MJ Dello Russo N DiSanti MA Magee-Sauer K Novak RE Brittain S Rettig T McLean IS Reuter DC Xu LH 《Science (New York, N.Y.)》2001,292(5520):1334-1339
In the current paradigm, Oort cloud comets formed in the giant planets' region of the solar nebula, where temperatures and other conditions varied greatly. The measured compositions of four such comets (Halley, Hyakutake, Hale-Bopp, and Lee) are consistent with formation from interstellar ices in the cold nebular region beyond Uranus. The composition of comet C/1999 S4 (LINEAR) differs greatly, which suggests that its ices condensed from processed nebular gas, probably in the Jupiter-Saturn region. Its unusual organic composition may require reevaluation of the prebiotic organic material delivered to the young Earth by comets. 相似文献
14.
Ishii HA Bradley JP Dai ZR Chi M Kearsley AT Burchell MJ Browning ND Molster F 《Science (New York, N.Y.)》2008,319(5862):447-450
The Stardust mission returned the first sample of a known outer solar system body, comet 81P/Wild 2, to Earth. The sample was expected to resemble chondritic porous interplanetary dust particles because many, and possibly all, such particles are derived from comets. Here, we report that the most abundant and most recognizable silicate materials in chondritic porous interplanetary dust particles appear to be absent from the returned sample, indicating that indigenous outer nebula material is probably rare in 81P/Wild 2. Instead, the sample resembles chondritic meteorites from the asteroid belt, composed mostly of inner solar nebula materials. This surprising finding emphasizes the petrogenetic continuum between comets and asteroids and elevates the astrophysical importance of stratospheric chondritic porous interplanetary dust particles as a precious source of the most cosmically primitive astromaterials. 相似文献
15.
Two isolated solar wind disturbances about 5 minutes in duration were detected aboard the Russian spacecraft Phobos-2 upon its crossing the wake of the martian moon Deimos about 15,000 kilometers downstream from the moon on 1 February 1989. These plasma and magnetic events are interpreted as the inbound and outbound crossings of a Mach cone that is formed as a result of an effective interaction of the solar wind with Deimos. Possible mechanisms such as remanent magnetization, cometary type interaction caused by heavy ion or charged dust production, and unipolar induction resulting from the finite conductivity of the body are discussed. Although none of the present models is fully satisfactory, neutral gas emission through water loss by Deimos at a rate of about 10(23) molecules per second, combined with a charged dust coma, is favored. 相似文献
16.
Ney EP 《Science (New York, N.Y.)》1977,195(4278):541-546
Infrared astronomy has shown that certain classes of stars are abundant producers of refractory grains, which condense in their atmospheres and are blown into interstellar space by the radiation pressure of these stars. Metallic silicates of the kind that produce terrestrial planets are injected by the oxygen-rich stars and carbon and its refractories by carbon stars. Much of the interstellar dust may be produced by this mechanism. A number of "infrared stars" are completely surrounded by their own dust, and a few of these exhibit a unique morphology that suggests the formation of a planetary system or a stage in the evolution of a planetary nebula. Certain novae also condense grains, which are blown out in their shells. In our own solar system, comets are found to contain the same silicates that are present elsewhere in the galaxy, suggesting that these constituents were present in the primeval solar nebula. 相似文献
17.
The application of crystal growth theory to the formation of smoke particles from the primordial solar nebula indicates that solid particles with filamentary structures would form. Such particles would facilitate successive aggregation into planets, comets, and asteroids. The difficulties associated with the aggregation of spherical smoke particles would thus be avoided. 相似文献
18.
CM Alexander R Bowden ML Fogel KT Howard CD Herd LR Nittler 《Science (New York, N.Y.)》2012,337(6095):721-723
Determining the source(s) of hydrogen, carbon, and nitrogen accreted by Earth is important for understanding the origins of water and life and for constraining dynamical processes that operated during planet formation. Chondritic meteorites are asteroidal fragments that retain records of the first few million years of solar system history. The deuterium/hydrogen (D/H) values of water in carbonaceous chondrites are distinct from those in comets and Saturn's moon Enceladus, implying that they formed in a different region of the solar system, contrary to predictions of recent dynamical models. The D/H values of water in carbonaceous chondrites also argue against an influx of water ice from the outer solar system, which has been invoked to explain the nonsolar oxygen isotopic composition of the inner solar system. The bulk hydrogen and nitrogen isotopic compositions of CI chondrites suggest that they were the principal source of Earth's volatiles. 相似文献
19.
Gladman B 《Science (New York, N.Y.)》2005,307(5706):71-75
Our planetary system is embedded in a small-body disk of asteroids and comets, vestigial remnants of the original planetesimal population that formed the planets. Once formed, those planets dispersed most of the remaining small bodies. Outside of Neptune, this process has left our Kuiper belt and built the Oort cloud, as well as emplacing comets into several other identifiable structures. The orbits in these structures indicate that our outer solar system's comet disk was shaped by a variety of different physical processes, which teach us about how the giant planets formed. Recent work has shown that the scattered disk is the most likely source of short-period comets. Moreover, a growing body of evidence indicates that the sculpting of the Kuiper belt region may have involved large-scale planetary migration, the presence of other rogue planetary objects in the disk, and/or the close passage of other stars in the Sun's birth cluster. 相似文献
20.
Alfvén H 《Science (New York, N.Y.)》1971,173(3996):522-525
Some consequences of Newtonian mechanics, previously overlooked, result in a new understanding of the behavior of small bodies in the solar system. Collisions between such bodies lead not to a scattering of these bodies over an increasing volume but instead to a contraction resulting in a "jet stream," with application to meteor streams and streams of asteroids. It is possible that comets are formed by bunching in such streams. 相似文献