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In addition to guiding the HST, the accuracy of FGS sensors makes them useful for high- precision


astrometric measurements. These measurements help scientists determine the precise positions and motions of stars. The FGS sensors can provide star positions about 10 times more precisely than measurements made with ground-based telescopes. Scientists use astro- metric measurements to help define wobble in the motion of stars that might indicate the presence of a planetary companion (below left). The motions of stars can also determine whether a star pair represents a true binary star system, or simply an optical binary.1 5


Aided by elements of oilfield technology, the Hubble Space Telescope continues its work today. Scientists are using instruments like the HST to search the far reaches of the universe and uncover secrets of the past while reaching into our future.


Asteroids—Up Close and Personal A little closer to home, technologies developed for oilfield use are helping scientists explore asteroids in our solar system. These large pieces of rock are primordial objects left over from the formation of the solar system. Some scientists have suggested that asteroids are the remains of a protoplanet that was destroyed in a massive collision. However, the prevailing view is that asteroids are leftover rocky matter that never successfully coalesced into planets. Scientists theorize that the planets of the solar system formed from a nebula of gas and dust that coalesced into a disk of dust grains


around the developing Sun. Within the disk, tiny dust grains coagulated into larger and larger bodies called planetesimals, many of which eventually accreted into planets over a period of 100 million years. However, beyond the orbit of Mars, gravitational interference from Jupiter prevented protoplanetary bodies from growing to diameters


larger [ 620 miles] .1 6


Most asteroids are concentrated in an orbital belt between Mars and Jupiter (below). These space rocks orbit the Sun as planets do, but they have no atmosphere and very little gravity. The asteroids in the belt comprise a significant


than about 1,000 km


A + Mars B Main +


asteroid b elt


Venus Earth Mercury


C + Troj an asteroids D + 0 1. 5 2. 7 Astronom ical units


> True b inary stars. Each of the tw o stars in a true b inary sy stem orb its around the center of m ass of the sy stem . K epler’ s law s of planetary


m otion govern how each star orb its the center of m ass. At aphelion ( A) , each of the tw o stars are the farthest apart in their respective orb its. At perihelion ( C) , the stars are the closest.


48


> Main asteroid b elt. The asteroid b elt is a region of the solar sy stem falling roughly b etw een the planets Mars and J upiter w here the greatest concentration of asteroid orb its can b e found. The m ain


b elt region contains approx im ately 9 3 . 4 % of all num b ered m inor planets. Troj an asteroids occupy tw o regions centered 60° ahead of and b ehind J upiter. Several hundred Troj ans are k now n out of a total population that includes an estim ated 2, 3 00 ob j ects b igger than 15 k m [ 9 m iles] across and m any m ore of sm aller size; m ost do not m ove in the plane of the planet’ s orb it b ut rather in orb its inclined b y up to 4 0° .


Oilfield Review 5 . 2 J upiter Troj an asteroids


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