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he Final Flight of a Sun-Diving Comet Carey M. Lisse Science 335, 296 (2012); DOI: 10.1126/science.1217168 This copy is for your personal, non-commercial use only. If you wish to distribute this article to others, you can order high-quality copies for your colleagues, clients, or customers by clicking here.
The Final Flight of a Sun-Diving Comet Carey M. Lisse Science 335, 296 (2012); DOI: 10.1126/science.1217168 This copy is for your personal, non-commercial use only. If you wish to distribute this article to others, you can order high-quality copies for your colleagues, clients, or customers by clicking here. Permission to republish or repurpose articles or portions of articles can be obtained by following the guidelines here. The following resources related to this article are available online at www.sciencemag.org (this infomation is current as of January 19, 2012 ): Downloaded from www.sciencemag.org on January 19, 2012 Updated information and services, including high-resolution figures, can be found in the online version of this article at: http://www.sciencemag.org/content/335/6066/296.full.html This article cites 10 articles, 2 of which can be accessed free: http://www.sciencemag.org/content/335/6066/296.full.html#ref-list-1 This article appears in the following subject collections: Planetary Science http://www.sciencemag.org/cgi/collection/planet_sci Science (print ISSN 0036-8075; online ISSN 1095-9203) is published weekly, except the last week in December, by the American Association for the Advancement of Science, 1200 New York Avenue NW, Washington, DC 20005. Copyright 2012 by the American Association for the Advancement of Science; all rights reserved. The title Science is a registered trademark of AAAS. PERSPECTIVES ASTRONOMY The Final Flight of a A suite of space-based observatories has captured the details of a comet as it disintegrates in the solar corona. Sun-Diving Comet Carey M. Lisse O ver the past decade, solar monitor- those fragments, may reveal details about the mass loss rates. The exact physical details of ing observatories have detected and sizes of the constituents from which the com- the process are still to be worked out—i.e., discovered more than 1600 discrete ets were formed. exactly what happens to a chunk of cometary members of the Kreutz family of comets. Schrijver et al. tracked comet C/2011 matter once it breaks off or is ejected from These comets are associated by common N3 (SOHO) and monitored its optical and the nucleus—but it is highly likely, as the orbits and their propensity to come within extreme-ultraviolet (EUV) emissions and authors argue, that the dominant mechanisms a few solar radii (RSun) of the Sun. They can absorptions as it passed at tremendous speed are related to coronal plasma collisions. By be detected as they evaporate and disinte- (~650 km/s) through the solar corona on 6 studying more passages of comets through Downloaded from www.sciencemag.org on January 19, 2012 grate, throwing out huge amounts of ﬁne dust July 2011 UT (Universal Time) only 100,000 the corona, both in new events [e.g., the and gas, which can be seen even against the km (~0.15 Rsun) above the Sun’s photosphere recent sun-diving passage of comet C/Love- Sun’s glare. Thought to be the fragmented (see the figure). The first observations of joy on 16 December 2011 (8)] and by search- remnants of the passage of a giant (~10 to their kind, the results pave the way for future ing through the archival SOHO, STEREO, 50 km radius) parent comet several thou- measurements of sungrazer cometary dis- and SDO records, we will increase our under- sand years ago, the Kreutz family has been integration times, length scales, masses and standing of how comets fall apart and are put the subject of intense study by both amateur and professional astrono- 1000 mers using a plethora of optical and ultraviolet instrumentation onboard a number of spacecraft designed to 00:01:12 study the Sun. On page 324 of this 23:59:36 23:57:00 issue, Schrijver et al. (1) report com- 23:56:00 800 bined observations from the Solar 23:51:36 23:49:48 Dynamics Observatory (SDO), the Solar Heliospheric Observa- tory (SOHO), and Solar-Terrestrial North to South (arc sec) Relations Observatory (STEREO) 600 detailing the path of comet C/2011 N3 (SOHO) as it passes through and disintegrates in the Sun’s lower corona. Such a method of cometary study may provide insight into the makeup of the parent body as well as 400 the constituent material of the early solar system. Some of the brightest comets ever seen have been large Kreutz sun- grazers—the Great Comets of 1106, 200 1843, 1882, and C/1965 Ikeya-Seki (2, 3); and there is a steady stream of smaller Kreutz fragments arriv- 0 200 400 600 800 1000 1200 ing more or less continuously. East to West (arc sec) The various pieces of the original Kreutz comet are estimated (4) to be A ﬂight path to destruction. Extreme-ultraviolet image of the solar corona (in SDO’s 171 Å channel, most sensitive to roughly the same size (~10 to 1000 emission from coronal plasma near 10 K), on 6 July 2011 00:00:01 UTC (coordinated UT). Overlaid (dashed-white box) 6 m in radius) as the fragments pro- is the projected orbit of the comet C/2011 N3 between 5 July 2011 23:46 UTC and 6 July 2011 00:06 UT. Insets (with duced by disrupting comets D/1999 UTC times) show a subframe region containing the comet nucleus, coma, and debris trail, after subtraction of the same CREDIT: C. J. SCHRIJVER ET AL. region imaged 36 s earlier to remove the background corona. The nucleus and coma region were found to be consistently S4 (LINEAR) (5) and 73P/Schwass- dark and EUV absorptive in all images; the trail was found to be EUV bright, likely due to energy deposition and heat- mann-Wachmann 3 (6, 7) and, like ing from collisions with the solar coronal plasma. Detailed modeling shows that the comet passed at perihelion through the closed-ﬁeld solar corona rather than through the solar wind, although the EUV-bright tail does not align with the John Hopkins University, Applied Physics Labo- observed coronal magnetic ﬁeld lines. The comet is moving from right to left across the face of the Sun in this image, ratory, Laurel, MD 20723, USA. E-mail: carey. and the nucleus is on the extreme left of each subframe; the debris trail is becoming fainter with time, as the comet dis- email@example.com sipates and disintegrates in the corona. One arc sec equals ~740 km. 296 20 JANUARY 2012 VOL 335 SCIENCE www.sciencemag.org Published by AAAS PERSPECTIVES together. The results from comet C/2011 N3 frequency distribution of sun-grazing comet quasi-static magnetohydrodynamic models (SOHO) are thus pioneering a new method of fragments may be able to provide important used in the past. Understanding how the roil- cometary study. information about the formation mechanisms ing 5780 K convective surface of the present- Understanding the physical construc- of comets. day Sun, perfused with magnetic ﬁeld lines tion of comets sheds important light on how Sun-grazing comets also probe a local extending out into interplanetary space, cre- matter accreted from tiny, micrometer-sized temperature regime, from 1000 to 4000 K, ates the ~106 K tenuous corona exosphere is specks of dust and molecules of gas to build that is not otherwise encountered in the solar not only the prime goal of NASA’s next big kilometer-sized ice and rock-rich bodies, the system, emitting material via sublimation and solar mission, Solar-Probe Plus, but is also comets, in the ﬁrst million years of the solar thermal desorption as they do so. Thus, from vital to our existence as human beings living system’s existence (9). This is still a great remote spectroscopic studies of sungrazers, 93 million miles away, as this is the region of mystery—most studies of the aggregation we can learn about the least-volatile compo- space where the giant solar ﬂares and coro- of protoplanetary gas and dust, using their nents that make up comets (and presumably nal mass ejections are created and launched known physical parameters (bulk modulus, the rest of the bodies in the solar system), like toward the planets. porosity, surface cohesion, dielectric con- the rocky silicates and metal sulﬁdes that are stant, etc.) at the expected interaction speeds some of the ﬁrst materials to condense out of References 1. C. J. Schrijver et al., Science 335, 324 (2012). of a few kilometers per second or more, show the protosolar nebula and protoplanetary disk 2. B. G. Marsden, Astron. J. 98, 2306 (1989). that particles should build up to millimeter- and make up the bulk of Earth and the other Downloaded from www.sciencemag.org on January 19, 2012 3. Z. Sekanina, P. W. Chodas, Astrophys. J. 607, 620 to centimeter-sized objects quite easily along terrestrial planets. (2004). the plane of the early solar system, but larger- The work of Schrijver et al. also holds 4. M. M. Knight et al., Astron. J. 139, 926 (2010). 5. H. A. Weaver et al., Science 292, 1329 (2001). sized particles disintegrate upon impact, cre- great promise for improving our understand- 6. H. A. Weaver et al., Bull. Am. Astron. Soc. 38, 490 (2006). ating an “aggregational barrier” to planetesi- ing of the solar corona. By using comets as 7. W. T. Reach, J. Vaubaillon, M. S. Kelley, C. M. Lisse, M. V. mal formation (10, 11). (On the other hand, standard test particles and “running” them Sykes, Icarus 203, 571 (2009). 8. http://science.nasa.gov/science-news/science-at- once billions of kilometer-sized comet bodies through the corona, observations of the pas- nasa/2011/16dec_cometlovejoy were formed, accretion into the known plan- sage of many comets at different heights 9. C. M. Lisse, Bull. Am. Astron. Soc. 42, 965 (2010). etary-sized objects was relatively straightfor- above the photosphere, at different times, 10. K. Wada, H. Tanaka, T. Suyama, H. Kimura, T. Yamamoto, Astrophys. J. 702, 1490 (2009). ward.) Since comets are weak bodies formed and in different solar latitudes and longi- 11. A. Zsom, C. W. Ormel, C. Güttler, J. Blum, C. P. Dullemond, relatively gently, it is likely they fragment tudes, will also help us to map out the three- Astron. Astrophys. 513, A57 (2010). and disrupt into pieces similar to those from dimensional density structure of the corona which they were assembled. Thus, the size- in a completely new way, independent of the 10.1126/science.1217168 GEOPHYSICS Transforming Earthquake Citizen science projects have the potential to transform earthquake science if data quality Detection? standards are maintained. Richard M. Allen E arthquakes are a collective experience. discovery, and what is the role of education? mation of each report is converted to lati- Citizens have long participated in Modern geophysical instruments can tude-longitude coordinates and the data are earthquake science through the report- record a magnitude 5 (M5) earthquake from mapped. Online tools allow users to explore ing, collection, and analysis of individual the other side of the world. However, to the data set that includes their contribution. experiences. The value of citizen-generated map, track, and analyze the details of large The project also has an educational compo- status reports was clear after the 1995 Kobe, destructive earthquake ruptures, and to elu- nent explaining earthquake phenomena. Japan, earthquake (1). Today’s communica- cidate how the rupture process links to earth- The DYFI database now contains nearly tions infrastructure has taken citizen engage- quake impacts, requires detailed data from 2 million entries available for download (8– ment to a new level: Earthquake-related Twit- close to the event. Currently, the best tradi- 10). The DYFI data are used to complement ter messages can outrun the shaking (2), tional geophysical networks only have sta- the traditional network data. Combined with Internet trafﬁc detects earthquakes (3–7) and tions every ~10 km and cover limited areas. reports of building damage, they can also maps the distribution of shaking in minutes Contributions of citizens have the potential help to determine how well building infra- (8–10), and accelerometers in consumer elec- to provide much higher resolution, especially structure can withstand earthquake shaking tronic devices record seismic waveforms (11– in residential areas. in different locations. 16). What are we learning from this ﬂood of The best-developed citizen-based earth- An individual’s reaction to an earthquake data, and what are the limitations? How do we quake science project today is the U.S. Geo- can also be tracked for scientiﬁc purposes harness these new capabilities for scientiﬁc logical Survey’s (USGS) “Did You Feel It?” without that individual’s active participation. (DYFI) (8–10). After an earthquake, indi- The European-Mediterranean Seismological Seismological Laboratory and Department of Earth and viduals can go online and answer questions Center (EMSC) tracks the hits on its Web site Planetary Science, University of California, Berkeley, CA designed to capture the data necessary to esti- and uses the hit rate and Internet protocol (IP) 94720, USA. E-mail: firstname.lastname@example.org mate shaking intensity. The location infor- addresses to extract information about earth- www.sciencemag.org SCIENCE VOL 335 20 JANUARY 2012 297 Published by AAAS
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