How long can the most extreme planetary systems survive? Measuring the tidal orbital decay of hot Jupiters.

最极端的行星系统能存活多久？

• 批准号: 446158000
• 负责人: Dr. Alexis Smith
• 金额: --
• 依托单位: Institut für Planetenforschung
• 依托单位国家: 德国
• 项目类别: Priority Programmes
• 资助国家: 德国
• 项目状态: 未结题
• 来源: https://gepris.dfg.de/gepris/projekt/446158000?language=en
• 关键词: How; long; most; extreme; planetary

For centuries, humanity has dreamed of planets beyond the Earth, and even beyond our Solar System. In 1995, these dreams started to become a reality, with the discovery of the first planet orbiting another star like our Sun. This exoplanet was remarkable because it looked very different to anything we were used to. The planet is a massive gas giant, similar to Jupiter, but takes just 4 days to complete an orbit of its star (contrast this with 88 days for Mercury, the closest planet to the Sun, and almost 12 years for Jupiter). Since then, many more such planets have been discovered, some even closer to their star (the record holder has an orbital period of just 18 hours). These exoplanets are known as 'hot Jupiters'.One of the biggest questions we have about these short-period hot Jupiters is how long they can survive so close to their host star (50 or more times closer than Earth is to the Sun). At these distances there are strong tidal forces at work between the planet and the star (rather like those in action between the Earth and the Moon). These forces cause the planet to lose energy which is transferred to the star. This loss of energy from the planetary orbit causes the planet's orbit to get gradually smaller, and the planet slowly spiral towards the star until it is destroyed. What we don't know is how fast this process of tidal orbital decay is. It might be that this happens relatively rapidly, with hot Jupiters only living for a few million or tens of millions of years, which is less than one percent of the star's lifetime. Alternatively, this slow dance of death might take billions of years, and so the life expectancy of a hot Jupiter would be similar to that of its star. This timescale is determined by a quantity Q*, which tells us how efficient a star is at absorbing the energy from a planet's orbit. Unfortunately, we don't know how big Q* is; in fact estimates vary hugely, which is what causes the enormous uncertainty in hot Jupiter lifetimes.This project aims to accurately measure Q* for several planetary systems. We will use exoplanets that pass directly in front of their host stars (transit) as viewed from Earth. Normally, we expect to observe these transits spaced at exactly regular intervals as the planet transits once per orbit. If the orbit is undergoing tidal decay, however, we expect to see the transits getting ever-so-slightly closer together. The effect is predicted to be just a few seconds shift, measured over a period of several years. This is, however, possible with modern telescopes, cameras and advanced data reduction and modelling techniques.Measuring Q* will not only tell us the life expectancy of hot Jupiters, it will also tell us about the timescales of other processes resulting from tidal interactions between star and planet. This will, for example, help us to determine how the hot Jupiters came to exist so close to their host stars when we think they must have formed further away, where it is cooler.

几个世纪以来，人类一直梦想着拥有地球之外、甚至太阳系之外的行星。 1995 年，随着发现第一颗围绕太阳这样的恒星运行的行星，这些梦想开始成为现实。这颗系外行星非常引人注目，因为它看起来与我们习惯的任何东西都非常不同。这颗行星是一颗巨大的气态巨行星，与木星类似，但只需 4 天即可完成绕恒星运行一周（相比之下，距太阳最近的行星水星需要 88 天，木星则需要近 12 年）。从那时起，更多的此类行星被发现，其中一些距离恒星更近（纪录保持者的轨道周期仅为 18 小时）。这些系外行星被称为“热木星”。关于这些短周期热木星，我们面临的最大问题之一是它们距离主恒星如此之近（比地球与太阳的距离近 50 倍或更多）能够存活多久。在这些距离上，行星和恒星之间存在强大的潮汐力（就像地球和月球之间的潮汐力一样）。这些力导致行星失去转移到恒星的能量。行星轨道的能量损失导致行星的轨道逐渐变小，行星慢慢地螺旋向恒星移动，直到被摧毁。我们不知道的是潮汐轨道衰减过程有多快。这种情况可能发生得相对较快，热木星的寿命只有几百万或几千万年，不到恒星寿命的百分之一。或者，这种缓慢的死亡之舞可能需要数十亿年，因此热木星的预期寿命将与其恒星的预期寿命相似。这个时间尺度由 Q* 量决定，它告诉我们恒星从行星轨道吸收能量的效率如何。不幸的是，我们不知道 Q* 有多大；事实上，估计值差异很大，这就是导致热木星寿命存在巨大不确定性的原因。该项目旨在准确测量几个行星系统的 Q*。我们将使用从地球上看直接经过其主恒星（凌日）前方的系外行星。通常，当行星每轨道凌日一次时，我们期望观察到这些凌日间隔完全规则的间隔。然而，如果轨道正在经历潮汐衰变，我们预计会看到凌日变得更加接近。经过几年的测量，预计效果只会有几秒钟的变化。然而，借助现代望远镜、相机以及先进的数据简化和建模技术，这是可能的。测量 Q* 不仅可以告诉我们热木星的预期寿命，还可以告诉我们由恒星和行星之间的潮汐相互作用产生的其他过程的时间尺度。例如，这将帮助我们确定热木星是如何与它们的主恒星如此接近地存在的，而我们认为它们一定是在距离更远、温度更低的地方形成的。