Spots on Ceres’ sur­face per­plex as­tro­physi­cists


First clas­si­fied a planet, then an as­ter­oid and then a “dwarf planet” with some traits of a moon — the more sci­en­tists learn about Ceres, the weirder it be­comes.

And new ob­ser­va­tions of the sphere of rock and ice cir­cling our sun be­tween Mars and Jupiter have added to the mys­tery, re­searchers said Mon­day.

As­tro­physi­cists have been look­ing to a US$473-mil­lion (446-mil­lion-euro) mission to test the­o­ries that Ceres is a wa­ter-rich plan­e­tary “em­bryo” — a relic from the birth of the So­lar Sys­tem some 4.5 bil­lion years ago.

But an early batch of data from NASA’s Dawn probe, un­veiled at a con­fer­ence of the Euro­pean Geo­sciences Union (EGU), may have made the Ceres rid­dle even greater.

In or­bit around Ceres since March 6 af­ter a seven-and-a-hal­fyear trek, Dawn peered at two bright spots on its sur­face deemed to be tell­tales of its chem­i­cal and phys­i­cal ID.

But in­stead of ex­plain­ing the spots, anal­y­sis found the two seemed to “be­have dis­tinctly dif­fer­ently,” said Fed­erico Tosi, who works on Dawn’s Vis­i­ble and Infrared Map­ping Spec­trom­e­ter (VIR).

While Spot 1 is colder than its im­me­di­ate sur­round­ings, Spot 5 is not.

The spots are two of a known dozen or so which on pho­to­graphs taken by Dawn re­sem­ble lights shin­ing on a dull grey sur­face.

Ceres trav­els at some 414 mil­lion kilo­me­ters (260 mil­lion miles) from the sun, tak­ing 4.61 Earth years to com­plete one or­bit.

About 950 kilo­me­ter ( 590 miles) wide, it is the big­gest ob­ject in the as­ter­oid belt — large enough for grav­ity to have molded its shape into a ball.

With VIR, the Dawn team have been able to put to­gether images at dif­fer­ent wave­lengths of light, Tosi told jour­nal­ists.

One pic­ture, as seen by the hu­man eye, shows Ceres as a “dark and brown­ish” ball with both white spots clearly vis­i­ble.

But in ther­mal images, Spot 1 be­comes a dark spot on a red­dish ball, in­di­cat­ing it was cooler than the rest of the sur­face, said Tosi.

The “big­gest sur­prise”, he added, was that Spot 5 sim­ply dis­ap­peared on the ther­mal im­age.

“For sure, we have bright spots on the sur­face of Ceres which, at least from a ther­mal per­spec­tive, seem to be­have in dif­fer­ent ways.”

The­o­ries about what the spots are range from ice to “hy­drated min­er­als” — wa­ter not in pure ice form but ab­sorbed by min­er­als.

Ice would be dif­fi­cult to ex­plain, though, as Ceres in­hab­its a zone not quite dis­tant enough from the sun to al­low “sta­ble ice” on the sur­face, said Tosi of the Na­tional In­sti­tute for As­tro­physics in Rome.

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