Multiple, quiet, and close by

doi:10.1126/science.abb0217

GSTDTAP > 气候变化

DOI	10.1126/science.abb0217
	Multiple, quiet, and close by
	Melvyn B. Davies
	2020-06-26
发表期刊	Science
出版年	2020
英文摘要	Planetary systems around stars are common, with many or most stars possessing them. On page 1477 of this issue, Jeffers et al. ([ 1 ][1]) report the discovery of a multiplanet system around the low-mass star GJ 887. GJ 887 is an unusual host star, as it is relatively inactive, and the planetary system happens to be very close to our Sun. This makes the system a good candidate for study with the to-be-launched James Webb Space Telescope (JWST). Stars form with a range of masses, the vast majority being less massive than the Sun. GJ 887 is a so-called red dwarf and has a mass of about one-half that of the Sun. Many red dwarfs are found to host planetary systems, typically containing multiple, low-mass planets ([ 2 ][2]). Two methods have been used to discover most planets. In the transit method, planets are found when they periodically block out a fraction of the starlight as they pass in front of their host star. This allows many stars to be searched for orbiting planets simultaneously. For example, some one hundred thousand stars were observed at the same time in the Kepler mission ([ 3 ][3]). However, for planets to be found in this way, their planetary orbits must be close to edge-on as seen from Earth in order for them to be seen to pass in front of their host star. This means that only a small fraction of planets will be found using this method. The planets around GJ 887 were discovered through a second approach: using the Doppler effect to measure the radial velocity of the host star over time. A planet and star orbit around a common center of mass, which means that the presence of a planet orbiting a star can be deduced by observing the periodic variation in the radial speed of the star. The radial velocity is measured from the Doppler shift of lines observed in the stellar spectra. Jeffers et al. observed GJ 887 nightly over a period of 3 months and combined their data with other observations. They found that GJ 887 has at least two planets, with orbital periods of 9.3 and 21.8 days, and a possible third planet farther out, with an orbital period of ∼50 days. GJ 887 is not unusual in possessing planets so close to it. Planets are generally believed to form farther away from their host star and migrate inward owing to a drag force from the protoplanetary disk from which they formed. As planets move inward, interactions between them can act to tune the ratio of their orbital periods, for example, leading to a 2:1 ratio where one planet goes around once in the time it takes the other to go around twice ([ 4 ][4]). ![Figure][5] A nearby planetary system The red dwarf star GJ 887 is only 11 light-years away from Earth and has at least two planets orbiting it. The potential location of a third planet, which needs confirmation, may lie in the habitable zone, where liquid water is stable on the surface. GRAPHIC: N. CARY/ CIENCE Planetary systems have been seen with neighboring planets in or close to these so-called orbital resonances. The TRAPPIST-1 system is a classic example of a set of planets in a resonance chain where all neighboring planets have periods with simple integer ratios ([ 5 ][6]). Planetary systems also appear to be full, with no room left for additional planets ([ 6 ][7]). The tugging and pulling of neighboring planets can act to change planetary orbits. This effect is damped out by the proto planetary gaseous disk. Once the disk is evaporated by the host star, the planetary system might become unstable, leading to planet scattering and collisions that leave a system with the planets no longer in resonance chains ([ 7 ][8]). This scenario may well have happened for GJ 887. The potential for life on any of the planets can be evaluated by looking at the likely surface conditions. The inner planets are probably too close to their host star, receiving about 2.5 and 8 times more energy from their host star than we receive from the Sun on Earth. However, red dwarfs are a good deal fainter than our own Sun, and the tentative third planet with a period of ∼50 days could be in the so-called habitable zone, where the surface temperature is suitable to allow liquid water ([ 8 ][9]). Solar flares and coronal mass ejections pose a serious threat to our life on Earth. For example, they could disrupt the electrical power supply grid. But serious events are rare, with the largest recent event striking Earth in 1859. Because red dwarfs have a higher magnetic activity, they have a much higher frequency of flares ([ 9 ][10]). Their flares can be lethal to life on planets in close orbit. But GJ 887 is a relatively inactive red dwarf, which makes the system particularly interesting. If someone had to live around a red dwarf, they would want to choose a quieter star like GJ 887. GJ 887 is also attractive to observe because, at a distance of only ∼11 lightyears, it is one of the closest planetary systems to Earth. This opens the prospect of atmospheric study of its planets by looking for reflected light from them using the JWST. These types of observations could tell us about the atmospheric makeup of these planets ([ 10 ][11]–[ 12 ][12]). If further observations confirm the presence of the third planet in the habitable zone, then GJ 887 could become one of the most studied planetary systems in the Solar neighborhood. 1. [↵][13]1. S. V. Jeffers et al ., Science 368, 1477 (2020). [OpenUrl][14][Abstract/FREE Full Text][15] 2. [↵][16]1. G. D. Mulders, 2. I. Pascucci, 3. D. Apai , Astrophys. J. 814, 130 (2015). [OpenUrl][17] 3. [↵][18]1. J. J. Lissauer et al ., Astrophys. J. Suppl. Ser. 197, 8 (2011). [OpenUrl][19][CrossRef][20] 4. [↵][21]1. G. A. L. Coleman, 2. R. P. Nelson , Mon. Not. R. Astron. Soc. 457, 2480 (2016). [OpenUrl][22][CrossRef][23] 5. [↵][24]1. M. Gillon et al ., Nature 542, 456 (2017). [OpenUrl][25][CrossRef][26][PubMed][27] 6. [↵][28]1. L. M. Weiss et al ., Astron. J. 155, 48 (2018). [OpenUrl][29] 7. [↵][30]1. B. Pu, 2. Y. Wu , Astrophys. J. 807, 44 (2015). [OpenUrl][31][CrossRef][32] 8. [↵][33]1. R. K. Kopparapu et al ., Astrophys. J. 765, 131 (2013). [OpenUrl][34][CrossRef][35] 9. [↵][36]1. K. France et al ., Astrophys. J. 820, 89 (2016). [OpenUrl][37][CrossRef][38] 10. [↵][39]1. L. Kreidberg, 2. A. Loeb , Astrophys. J. 832, L12 (2016). [OpenUrl][40] 11. 1. I. A. G. Snellen et al ., Astron. J. 154, 77 (2017). [OpenUrl][41][CrossRef][42] 12. [↵][43]1. E. M. R. Kempton et al ., Publ. Astron. Soc. Pac. 130, 114401 (2018). [OpenUrl][44][CrossRef][45] Acknowledgments: M.B.D. is supported by the project grant 2014.0017 “IMPACT” from the Knut and Alice Wallenberg Foundation. [1]: #ref-1 [2]: #ref-2 [3]: #ref-3 [4]: #ref-4 [5]: pending:yes [6]: #ref-5 [7]: #ref-6 [8]: #ref-7 [9]: #ref-8 [10]: #ref-9 [11]: #ref-10 [12]: #ref-12 [13]: #xref-ref-1-1 "View reference 1 in text" [14]: {openurl}?query=rft.jtitle%253DScience%26rft.stitle%253DScience%26rft.aulast%253DJeffers%26rft.auinit1%253DS.%2BV.%26rft.volume%253D368%26rft.issue%253D6498%26rft.spage%253D1477%26rft.epage%253D1481%26rft.atitle%253DA%2Bmultiplanet%2Bsystem%2Bof%2Bsuper-Earths%2Borbiting%2Bthe%2Bbrightest%2Bred%2Bdwarf%2Bstar%2BGJ%2B887%26rft_id%253Dinfo%253Adoi%252F10.1126%252Fscience.aaz0795%26rft.genre%253Darticle%26rft_val_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Ajournal%26ctx_ver%253DZ39.88-2004%26url_ver%253DZ39.88-2004%26url_ctx_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Actx [15]: /lookup/ijlink/YTozOntzOjQ6InBhdGgiO3M6MTQ6Ii9sb29rdXAvaWpsaW5rIjtzOjU6InF1ZXJ5IjthOjQ6e3M6ODoibGlua1R5cGUiO3M6NDoiQUJTVCI7czoxMToiam91cm5hbENvZGUiO3M6Mzoic2NpIjtzOjU6InJlc2lkIjtzOjEzOiIzNjgvNjQ5OC8xNDc3IjtzOjQ6ImF0b20iO3M6MjM6Ii9zY2kvMzY4LzY0OTgvMTQzMi5hdG9tIjt9czo4OiJmcmFnbWVudCI7czowOiIiO30= [16]: #xref-ref-2-1 "View reference 2 in text" [17]: {openurl}?query=rft.jtitle%253DAstrophys.%2BJ.%26rft.volume%253D814%26rft.spage%253D130%26rft.genre%253Darticle%26rft_val_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Ajournal%26ctx_ver%253DZ39.88-2004%26url_ver%253DZ39.88-2004%26url_ctx_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Actx [18]: #xref-ref-3-1 "View reference 3 in text" [19]: {openurl}?query=rft.jtitle%253DAstrophys.%2BJ.%2BSuppl.%2BSer.%26rft.volume%253D197%26rft.spage%253D8%26rft_id%253Dinfo%253Adoi%252F10.1088%252F0067-0049%252F197%252F1%252F8%26rft.genre%253Darticle%26rft_val_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Ajournal%26ctx_ver%253DZ39.88-2004%26url_ver%253DZ39.88-2004%26url_ctx_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Actx [20]: /lookup/external-ref?access_num=10.1088/0067-0049/197/1/8&link_type=DOI [21]: #xref-ref-4-1 "View reference 4 in text" [22]: {openurl}?query=rft.jtitle%253DMon.%2BNot.%2BR.%2BAstron.%2BSoc.%26rft_id%253Dinfo%253Adoi%252F10.1093%252Fmnras%252Fstw149%26rft.genre%253Darticle%26rft_val_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Ajournal%26ctx_ver%253DZ39.88-2004%26url_ver%253DZ39.88-2004%26url_ctx_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Actx [23]: /lookup/external-ref?access_num=10.1093/mnras/stw149&link_type=DOI [24]: #xref-ref-5-1 "View reference 5 in text" [25]: {openurl}?query=rft.jtitle%253DNature%26rft.volume%253D542%26rft.spage%253D456%26rft_id%253Dinfo%253Adoi%252F10.1038%252Fnature21360%26rft_id%253Dinfo%253Apmid%252F28230125%26rft.genre%253Darticle%26rft_val_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Ajournal%26ctx_ver%253DZ39.88-2004%26url_ver%253DZ39.88-2004%26url_ctx_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Actx [26]: /lookup/external-ref?access_num=10.1038/nature21360&link_type=DOI [27]: /lookup/external-ref?access_num=28230125&link_type=MED&atom=%2Fsci%2F368%2F6498%2F1432.atom [28]: #xref-ref-6-1 "View reference 6 in text" [29]: {openurl}?query=rft.jtitle%253DAstron.%2BJ.%26rft.volume%253D155%26rft.spage%253D48%26rft.genre%253Darticle%26rft_val_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Ajournal%26ctx_ver%253DZ39.88-2004%26url_ver%253DZ39.88-2004%26url_ctx_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Actx [30]: #xref-ref-7-1 "View reference 7 in text" [31]: {openurl}?query=rft.jtitle%253DAstrophys.%2BJ.%26rft.volume%253D807%26rft.spage%253D44%26rft_id%253Dinfo%253Adoi%252F10.1088%252F0004-637X%252F807%252F1%252F44%26rft.genre%253Darticle%26rft_val_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Ajournal%26ctx_ver%253DZ39.88-2004%26url_ver%253DZ39.88-2004%26url_ctx_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Actx [32]: /lookup/external-ref?access_num=10.1088/0004-637X/807/1/44&link_type=DOI [33]: #xref-ref-8-1 "View reference 8 in text" [34]: {openurl}?query=rft.jtitle%253DAstrophys.%2BJ.%26rft.volume%253D765%26rft.spage%253D131%26rft_id%253Dinfo%253Adoi%252F10.1088%252F0004-637X%252F765%252F2%252F131%26rft.genre%253Darticle%26rft_val_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Ajournal%26ctx_ver%253DZ39.88-2004%26url_ver%253DZ39.88-2004%26url_ctx_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Actx [35]: /lookup/external-ref?access_num=10.1088/0004-637X/765/2/131&link_type=DOI [36]: #xref-ref-9-1 "View reference 9 in text" [37]: {openurl}?query=rft.jtitle%253DAstrophys.%2BJ.%26rft.volume%253D820%26rft.spage%253D89%26rft_id%253Dinfo%253Adoi%252F10.3847%252F0004-637X%252F820%252F2%252F89%26rft.genre%253Darticle%26rft_val_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Ajournal%26ctx_ver%253DZ39.88-2004%26url_ver%253DZ39.88-2004%26url_ctx_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Actx [38]: /lookup/external-ref?access_num=10.3847/0004-637X/820/2/89&link_type=DOI [39]: #xref-ref-10-1 "View reference 10 in text" [40]: {openurl}?query=rft.jtitle%253DAstrophys.%2BJ.%26rft.volume%253D832%26rft.spage%253DL12%26rft.genre%253Darticle%26rft_val_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Ajournal%26ctx_ver%253DZ39.88-2004%26url_ver%253DZ39.88-2004%26url_ctx_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Actx [41]: {openurl}?query=rft.jtitle%253DAstron.%2BJ.%26rft.volume%253D154%26rft.spage%253D77%26rft_id%253Dinfo%253Adoi%252F10.3847%252F1538-3881%252Faa7fbc%26rft.genre%253Darticle%26rft_val_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Ajournal%26ctx_ver%253DZ39.88-2004%26url_ver%253DZ39.88-2004%26url_ctx_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Actx [42]: /lookup/external-ref?access_num=10.3847/1538-3881/aa7fbc&link_type=DOI [43]: #xref-ref-12-1 "View reference 12 in text" [44]: {openurl}?query=rft.jtitle%253DPubl.%2BAstron.%2BSoc.%2BPac.%26rft.volume%253D130%26rft.spage%253D114401%26rft_id%253Dinfo%253Adoi%252F10.1088%252F1538-3873%252Faadf6f%26rft.genre%253Darticle%26rft_val_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Ajournal%26ctx_ver%253DZ39.88-2004%26url_ver%253DZ39.88-2004%26url_ctx_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Actx [45]: /lookup/external-ref?access_num=10.1088/1538-3873/aadf6f&link_type=DOI
领域	气候变化 ; 资源环境
URL	查看原文
引用统计
文献类型	期刊论文
条目标识符	http://119.78.100.173/C666/handle/2XK7JSWQ/278205
专题	气候变化资源环境科学
推荐引用方式 GB/T 7714	Melvyn B. Davies. Multiple, quiet, and close by[J]. Science,2020.
APA	Melvyn B. Davies.(2020).Multiple, quiet, and close by.Science.
MLA	Melvyn B. Davies."Multiple, quiet, and close by".Science (2020).