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The most comprehensive search for organics in the Martian soil was performed by the Viking Landers. Martian soil was subjected to a thermal volatilization process to vaporize and break organic molecules, and the resultant gases and volatiles were analyzed by gas chromatography‐mass spectrometry. Only water at 0.1–1.0 wt% was detected, with traces of chloromethane at 15 ppb, at Viking landing site 1, and water at 0.05–1.0 wt% and carbon dioxide at 50–700 ppm, with traces of dichloromethane at 0.04–40 ppb, at Viking landing site 2. These chlorohydrocarbons were considered to be terrestrial contaminants, although they had not been detected at those levels in the blank runs. Recently, perchlorate was discovered in the Martian Arctic soil by the Phoenix Lander. Here we show that when Mars‐like soils from the Atacama Desert containing 32 ± 6 ppm of organic carbon are mixed with 1 wt% magnesium perchlorate and heated, nearly all the organics present are decomposed to water and carbon dioxide, but a small amount is chlorinated, forming 1.6 ppm of chloromethane and 0.02 ppm of dichloromethane at 500°C. A chemical kinetics model was developed to predict the degree of oxidation and chlorination of organics in the Viking oven. Reinterpretation of the Viking results therefore suggests ≤0.1% perchlorate and 1.5–6.5 ppm organic carbon at landing site 1 and ≤0.1% perchlorate and 0.7–2.6 ppm organic carbon at landing site 2. The detection of organics on Mars is important to assess locations for future experiments to detect life itself.

The weak, R‐type ionization fronts (I‐fronts) which swept across the intergalactic medium during the reionization of the Universe often found their paths blocked by cosmological minihaloes (haloes with virial temperatures Tvir≤ 104 K). When this happened, the neutral gas which filled each minihalo was photoevaporated. In a cold dark matter universe, minihaloes formed in abundance before and during reionization and, thus, their photoevaporation is an important, possibly dominant, feature of reionization, which slowed it down and cost it many ionizing photons. In a previous paper, we described this process and presented our results of the first simulations of it by numerical gas dynamics with radiation transport in detail. In view of the importance of minihalo photoevaporation, both as a feedback mechanism on the minihaloes and as an effect on cosmic reionization, we have now performed a larger set of high‐resolution simulations to determine and quantify the dependence of minihalo photoevaporation times and photon consumption rates on halo mass, redshift, ionizing flux level and spectrum. We use these results to derive simple expressions for the dependence of the evaporation time and photon consumption rate on these halo and external flux parameters. These can be conveniently applied to estimate the effects of minihaloes on the global reionization process in both semi‐analytical calculations and larger‐scale, lower‐resolution numerical simulations, which cannot adequately resolve the minihaloes and their photoevaporation. We find that the average number of ionizing photons each minihalo atom absorbs during its photoevaporation is typically in the range 2–10. For the collapsed fraction in minihaloes expected during reionization, this can add about one photon per total atom to the requirements for completing reionization, potentially doubling the minimum number of photons required to reionize the Universe.

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Planet formation is believed to occur in the disks of gas and dust that surround young solar-type stars 1 . Most stars, however, form in multiple systems 2-5 , where the presence of a close companion could affect the structure of the disk 6-8 and perhaps interfere with planet formation. It has been difficult to investigate this because of the resolution needed. Here we report interferometric observations (at a wavelength of 7 mm) of the core of the star-forming region L1551. We have achieved a linear resolution of seven astronomical units (less than the diameter of Jupiter's orbit). The core of L1551 contains two distinct disks, with a separation of 45 AU; these appear to be associated with a binary system. Both disks are spatially resolved, with semi-major axes of about 10 AU, which is about a factor of ten smaller than disks around isolated stars 9-12 . The disk masses are of order 0.05 solar masses, which could be enough to form planetary systems like our own.L1551 is a molecular cloud in Taurus that is known to be undergoing intensive star formation, although restricted to lowmass stars (that is, with masses comparable to or smaller than that of the Sun). The embedded infrared source L1551 IRS5 (ref. 13) is believed to be associated with a very young stellar source. Its bolometric luminosity is ϳ30 solar luminosities 14 and it is embedded in a dense envelope of molecular gas and dust that extends over ϳ10 3 -10 4 AU (refs 15, 16). The continuum millimetre emission, when observed with angular resolutions of ϳ1 arcsec, has been interpreted as originating from heated dust in a protoplanetary disk with dimensions of about 100 AU (refs 17, 18).In the centimetre wavelengths, there is compact radio continuum emission with elongated morphology 19,20 that aligns with the largescale bipolar molecular outflow 21 . This centimetre radiation is known to be free-free emission that originates in the ionized outflowing gas 22 . However, when observed with subarc second angular resolution, the core of the centimetre emission from L1551 IRS5 breaks into two compact components separated by 0.3 arcsec, which have been interpreted as being either a protobinary system 19 or the inner ionized edges of a gas and dust toroid around a single star 20 . As the millimetre continuum emission, tracing the dust, has been interpreted as coming from a single disk, the singlestar interpretation has been favoured recently. However, there are several observations that suggest that two independent outflow systems emanate from L1551 IRS5 (refs 23-25), favouring a binary nature for the source. Furthermore, observations at 2.7-mm (ref. 26) with angular resolution of about 0.5 arcsec have been used to argue for the presence of two unresolved disks in L1551 IRS5.Our observations were made with the Very Large Array of the National Radio Astronomy Observatory in its highest angular resolution A configuration. The 7-mm observations were made in 1997 January 10, and the 3.6-cm observations were made in 1996 December 10. As the observations are separated b...

We present [S ii] images of the HH 30 and HL/XZ Tau region obtained at two epochs, as well as long-slit optical spectroscopy of the HH 30 jet. We measured proper motions of $100Y300 km s À1 for the HH 30 jet and counterjet and of $120 km s À1 for the HL Tau jet. Inclination angles with respect to the plane of the sky are 0 Y40 for the HH 30 jet and 60 for the HLTau jet. Comparison with previous observations suggests that most of the jet knots consist of persistent structures. Also, we corroborate that the HH 30-N knots correspond to the head of the HH 30 jet. The overall HH 30 jet structure can be well described by a wiggling ballistic jet, arising either from orbital motion of the jet source around a primary or from precession of the jet axis because of the tidal effects of a companion. In the first scenario, the orbital period would be 53 yr and the total mass 0.25Y2 M . In the precession scenario, the mass of the jet source would be $0.1Y1 M , the orbital period <1 yr, and the mass of the companion less than a few times 0.01 M , thus being a substellar object or a giant exoplanet. In both scenarios a binary system with a separation <18 AU (<0.13 00 ) is required. Since the radius of the flared disk observed with the HST is $250 AU, we conclude that this disk appears to be circumbinary rather than circumstellar, suggesting that the search for the collimating agent of the HH 30 jet should be carried out at much smaller scales.