Rogue planets have been ejected from their planetary system. We investigate the possibility that a rogue planet could maintain a liquid ocean under layers of thermally-insulating water ice and frozen atmosphere as a result of geothermal heat flux. We find that a rogue planet of Earth-like composition and age could maintain a subglacial liquid ocean if it were ~3.5 times more massive than Earth. If a rogue planet had about ten times higher water mass fraction or a thick cryo-atmospheric layer, it would need to be only ~0.3 times the mass of Earth to maintain a liquid ocean. Such a planet could be detected from reflected solar radiation and its thermal emission could be characterized in the far-IR if it passed within O(1000) AU of Earth.
Time is arguably the key limiting factor for interstellar exploration. At high speeds, flyby missions to nearby stars by laser propelled wafersats taking 50-100 years would be feasible. Directed energy launch systems could accelerate on the other side also crafts weighing several tons to cruising speeds of the order of 1000\,km/s (c/300). At these speeds, superconducting magnetic sails would be able to decelerate the craft by transferring kinetic energy to the protons of the interstellar medium. A tantalizing perspective, which would allow interstellar probes to stop whenever time is not a lim…
The recent discovery of a staggering diversity of planets beyond the Solar System has brought with it a greatly expanded search space for habitable worlds. The Kepler exoplanet survey has revealed that most planets in our interstellar neighborhood are larger than Earth and smaller than Neptune. Collectively termed super-Earths and mini-Neptunes, some of these planets may have the conditions to support liquid water oceans, and thus Earth-like biology, despite differing in many ways from our own planet. In addition to their quantitative abundance, super-Earths are relatively large and are thus m…
Habitable Evaporated Cores and the Occurrence of Panspermia near the Galactic Center
黑洞通过气体的吸积而成长，释放出的辐射可以使附近行星的大气层光蒸发。在这里，我们夫妇的行星结构演化模型的亚海王星质量行星的银河系的中央超大质量黑洞，Sgr A $^*$的增长和研究如何行星演化的类星体活动的影响。我们发现，从Sgr A $^*$到${\sim} 20$ pc，在类星体阶段发射的XUV通量可以去除行星质量的百分之几的H/He包层;在许多情况下，这种去除导致裸露的岩石核心，其中许多位于G型恒星的宜居带（HZ）。亚海王星大小的行星的侵蚀可能是在银河系中心附近产生陆地超级地球的最普遍的渠道之一。因此，行星人口统计学在Sgr A $^*$附近可能与银河系外围大不相同。这一区域的恒星密度很高（大约比太阳附近的恒星密度高7个数量级），这意味着相邻的岩石世界之间的距离很短（$500-5000$ ~AU）。潜在的可居住的类地行星之间的接近可能使星系核附近广泛的星际胚种论的开始。更一般地说，我们预测这些现象在核星团和超致密矮星中的行星中无处不在。另一方面，球状星团受黑洞的影响较小。
The detection of exoplanets orbiting other stars has revolutionized our view of the cosmos. First results suggest that it is teeming with a fascinating diversity of rocky planets, including those in the habitable zone. Even our closest star, Proxima Centauri, harbors a small planet in its habitable zone, Proxima b. With the next generation of telescopes, we will be able to peer into the atmospheres of rocky planets and get a glimpse into other worlds. Using our own planet and its wide range of biota as a Rosetta stone, we explore how we could detect habitability and signs of life on exoplanets…
In the science fiction film $Interstellar$, a band of intrepid astronauts sets out to explore a system of planets orbiting a supermassive black hole, searching for a world that may be conducive to hosting human life. While the film legitimately boasts a relatively high level of scientific accuracy, it is still restricted by Hollywood sensitivities and limitations. In this paper, we discuss a number of additional astrophysical effects that may be important in determining the (un)inhabitable environment of a planet orbiting close to a giant, accreting black hole. Foremost among these effects is …
The ease of interstellar rocket travel is an issue with implications for the long term fate of our own and other civilizations and for the much-debated number of technological civilizations in the Galaxy. We show that the physical barrier to interstellar travel can be greatly reduced if voyagers are patient, and wait for the close passage of another star. For a representative time of $\sim$1 Gyr, characteristic of the remaining time that Earth will remain habitable, one anticipates a passage of another star within $\sim 1500$~AU. This lowers the travel time for interstellar migration by $\sim$…
The similarity of Venus and Earth in bulk properties make Venus an appealing target for future colonization. Several proposals have been put forward for colonizing and even terraforming Venus despite the extreme conditions on the planet's surface. Such a terraforming project would face large challenges centered around removing Venus's massive carbon dioxide atmosphere and replacing it with a habitable environment. I review past proposals and propose a new method for terraforming Venus by building an artificial surface in the much more hospitable upper atmosphere where the temperature and press…
