Comet Surface Wild and Crazy

first_img“Completely unexpected,” was the reaction of Donald Brownlee, principal investigator of the Stardust mission, to the photos revealed by the spacecraft that flew into the tail of Comet Wild-2 last January (see 01/02/2004 headline), reports a University of Washington press release.  The comet mission is the cover story in the June 18 issue of Science, with four scientific papers and two reviews.  Photos and information have also been released at the Jet Propulsion Laboratory Stardust website.    Scientists expected to find a dirty, fluffy snowball of loose material, but found instead a surface unlike anything else in the solar system.  Deep flat-floored pits, craters with steep walls and pinnacles more than three hundred feet high indicate that the comet material is rigid and cohesive enough, despite the low gravity, to hold together under impacts.  Planetary scientists thought that most comets were like rubble piles loosely held together by gravity, easily torn apart by gravitational perturbations.  Maybe some are, but the sharp edges, angular shapes and steep cliffs on Wild-2 make it look brittle and very unlike an asteroid, and different than the previously-visited comets Halley and Borrelly.  Perhaps there is more variety among comets than expected.    The comet jets on Wild-2 (pronounced vilt-2), also unexpectedly, emerge at high velocity from numerous places around the roughly circular body, rather than being sublimated off the outer surface volatiles.  Some of them appear to be collimated like the jets from a fire hose, suggesting that they emerge from pits deep in the interior.  Stardust was hit with two wallops as high-velocity dust particles from particularly strong jets pummeled its shields at hundreds of kilometers per hour on the way through the dust tail.  The spacecraft succeeded admirably, despite the hazards, in taking pictures and collecting dust particles in its aerogel collector for return to earth.    Delighted, but perplexed, describes the mood of scientists over the mission so far.  “New in situ observations of a comet are demonstrating once again how little we understand about these dark and mysterious planetesimals,” remarked Harold Weaver in Science.1  Brownlee et al.2 claim that the surface reveals a “juxtaposition of features that are young and old” on an object thought to be a primordial relic of the formation of the solar system.  Hinting that these findings are putting theories in turmoil, an editorial in the same issue3 hopes that the return of the particles in January 2006 will “clear up any nightmares about the origin of the solar system and the dynamics of comets.”1Harold A. Weaver, “Not a Rubble Pile?” Science, Vol 304, Issue 5678, 1760-1762, 18 June 2004 [DOI: 10.1126/science.1100581].2Brownlee et al., “Surface of Young Jupiter Family Comet 81P/Wild 2: View from the Stardust Spacecraft,” Science, Vol 304, Issue 5678, 1764-1769, 18 June 2004 [DOI: 10.1126/science.1097899].3“Sweet Dreams Are Made of These,” Science, Vol 304, Issue 5678, 1760, 18 June 2004 [DOI: 10.1126/science.304.5678.1760a].Everyone should be thrilled at the success of this mission of discovery, but it does point out a lesson about scientists.  Since scientists know so little about things they can observe, and since they often find contradictions to their expectations, why should we trust any confident-sounding pronouncements about things they can’t observe?  When they talk about this comet having formed billions of years ago, how can they possibly know that?    Brownlee’s paper says, “Pinnacles were not anticipated land forms on primitive bodies, and their origin on Wild 2 is a mystery.”  He thinks the jets, pinnacles and impact craters are young, but the rest of the comet is old, only because current theories require the solar system to be 4.6 billion years old, and comets had to form near the beginning.  But then how does he keep the comet from dissipating away completely long ago?  (See 03/27/2003 headline.)  He tells an ad hoc story to get the theory to fit the observations.  He claims Wild-2 may have repeatedly come inside Jupiter’s orbit and back out again.  But then how did the comet escape complete break-up by a collision in the planetary shooting gallery, or avoid getting ejected out of the solar system entirely, during one of those excursions?    The nightmares may not go away entirely in January 2006.  If history is any guide, the comet dust samples will answer some questions but raise many others.  For a sweet dream, however, imagine yourself standing on the surface of the three-mile wide comet.  The gravity is so low, you could jump and launch yourself into orbit.  Cool.(Visited 9 times, 1 visits today)FacebookTwitterPinterestSave分享0last_img read more

South Africa to speed up land reform

first_img25 February 2013 With South Africa set to mark the centenary of the notorious 1913 Land Act this year, the government is taking a number of steps to speed up land reform – including a shift from the “willing buyer, willing seller” to the “just and equitable” principle for compensation for land acquired by the state. In his State of the Nation Address to Parliament earlier this month, President Jacob Zuma announced that government would now pursue the “just and equitable” principle set out in the Constitution, instead of the “willing buyer, willing seller” principle which forces the state to pay more for land than its actual value. Zuma also announced proposed amendments to the Restitution of Land Rights Act to provide for the re-opening of the lodgement of restitution claims by people who missed the 31 December 1998 deadline. “Also to be explored are exceptions to the June 1913 cut-off date [i.e., claims for land confiscated before 1913] to accommodate claims by the descendants of the Khoi and San as well as heritage sites and historical landmarks.” Zuma said the government would also need to provide better incentives for commercial farmers that were willing to mentor smallholder farmers.Land redistribution Speaking during the debate on Zuma’s State of the Nation Address in Parliament last week, Rural Development and Land Reform Minister Gugile Nkwinti said farms transferred to black people through various redistribution programmes, from 1994 until January this year, amounted to 4 813 farms. This translated to 4.123-million hectares, benefiting 230 886 persons. He said a total of 50 440 beneficiaries were women (1.7-million hectares in the hands of women), while 32 563 were young people, and 674 were persons with disability. Nkwinti said the state had spent R12.9-billion on land. Of the 4.123 million hectares acquired, the government had, since 2010, recapitalised 696 farms into full operation, employing 4 982 permanent workers and investing R1.8-billion in infrastructure, inputs and strategic support. Of the 696 recapitalised farms, he said 332 were cropping and 364 were livestock farms. The gross income generated by these farms, as of 31 January 2013, was R126-million.Land restitution “Land acquired by the state for the restitution of land rights, since the inception of the programme [in 1995], amounts to 4 001 land parcels, translating into 1.443-million hectares,” Nkwinti said. “Of these beneficiaries, 136 968 are female-headed households, and 672 persons with disability have benefited. A total of R16-billion has been spent on the programme thus far. This in settling 77 148 claims; R10 billion for land acquisition, and R6 billion for 71 292 financial compensation claims.” Nkwinti said the 5 856 settled claims, translating into 1.443 million hectares, was land restored. He said this clearly illustrated that claimants had chosen financial compensation over land restoration, which was a reflection of poverty and unemployment. Nkwinti said a team of lawyers was working on the re-opening of land claims and addition of claims for land confiscated before 1913. The re-opening of lodgment of claims would take place once amendments to the Restitution of Land Rights Act had been signed into law by President Zuma. Source: SAnews.gov.zalast_img read more