Artist’s impression of Proxima b, which was discovered using the Radial Velocity method. Credit: ESO/M. Kornmesser
Welcome back to our series on Exoplanet-Hunting methods! Today, we look at another widely-used and popular method of exoplanet detection, known as the Radial Velocity (aka. Doppler Spectroscopy) Method.
The hunt for extra-solar planets sure has heated up in the past decade or so! Thanks to improvements made in instrumentation and methodology, the number of exoplanets discovered (as of December 1st, 2017) has reached 3,710 planets in 2,780 star systems, with 621 system boasting multiple planets. Unfortunately, due to the limits astronomers are forced to contend with, the vast majority have been discovered using indirect methods.
When it comes to these indirect methods, one of the most popular and effective is the Radial Velocity Method – also known as Doppler Spectroscopy. This method relies on observing the spectra stars for signs of “wobble”, where the star is found to be moving towards and away from Earth. This movement is caused by the presence of planets, which exert a gravitational influence on their respective sun.
In a series of papers, Professor Loeb and Michael Hippke indicate that conventional rockets would have a hard time escaping from certain kinds of extra-solar planets. Credit: NASA/Tim Pyle
With every passing year, more and more extra-solar planets are discovered. To make matters more interesting, improvements in methodology and technology are allowing for the discovery of more planets within individual systems. Consider the recent announcement of a seven-planet system around the red dwarf star known as TRAPPIST-1. At the time, this discovery established the record for most exoplanets orbiting a single star.
Well move over TRAPPIST-1! Thanks to the Kepler Space Telescope and machine learning, a team from Google AI and the Harvard-Smithsonian Center of Astrophysics (CfA) recently discovered an eighth planet in the distant star system of Kepler-90. Known as Kepler -90i, the discovery of this planet was made possible thanks to Google algorithms that detected evidence of a weak transit signal in the Kepler mission data.
Most exoplanets orbit red dwarf stars because they're the most plentiful stars. This is an artist's illustration of what the TRAPPIST-1 system might look like from a vantage point near planet TRAPPIST-1f (at right). Credits: NASA/JPL-Caltech
In February of 2017, NASA scientists announced the existence of seven terrestrial (i.e. rocky) planets within the TRAPPIST-1 star system. Since that time, the system has been the focal point of intense research to determine whether or not any of these planets could be habitable. At the same time, astronomers have been wondering if all of the system’s planets are actually accounted for.
For instance, could this system have gas giants lurking in its outer reaches, as many other systems with rocky planets (for instance, ours) do? That was the question that a team of scientists, led by researchers from the Carnegie Institute of Science, sought to address in a recent study. According to their findings, TRAPPIST-1 may be orbited by gas giants at a much-greater distance than its seven rocky planets.
This artist’s impression shows the view from the surface of one of the planets in the TRAPPIST-1 system. A powerful laser beacon using current and near-future technology could send a signal strong enough to be detected by any alien astronomers here. Credit: NASA/ESA/HST
In February of 2017, astronomers from the European Southern Observatory (ESO) announced the discovery of seven rocky planets around the nearby star of TRAPPIST-1. Not only was this the largest number of Earth-like planets discovered in a single star system to date, the news was also bolstered by the fact that three of these planets were found to orbit within the star’s habitable zone.
Since that time, multiple studies have been conducted to ascertain the likelihood that these planets are actually habitable. Thanks to an international team of scientists who used the Hubble Space Telescope to study the system’s planets, we now have the first clues as to whether or not water (a key ingredient
Most exoplanets orbit red dwarf stars because they're the most plentiful stars. This is an artist's illustration of what the TRAPPIST-1 system might look like from a vantage point near planet TRAPPIST-1f (at right). Credits: NASA/JPL-Caltech
In February of 2017, a team of European astronomers announced the discovery of a seven-planet system orbiting the nearby star TRAPPIST-1. Aside from the fact that all seven planets were rocky, there was the added bonus of three of them orbiting within TRAPPIST-1’s habitable zone. As such, multiple studies have been conducted that have sought to determine whether or not any planets in the system could be habitable.
When it comes to habitability studies, one of the key factors to consider is the age of the star system. Basically, young stars have a tendency to flare up and release harmful bursts of radiation while planets that orbit older stars have been subject to radiation for longer periods of time. Thanks to a new study by a pair of astronomers, it is now known that the TRAPPIST-1 system is twice as old as the Solar System.
Artist's concept of the TRAPPIST-1 star system, an ultra-cool dwarf that has seven Earth-size planets orbiting it. We're going to keep finding more and more solar systemsl like this, but we need observatories like WFIRST, with starshades, to understand the planets better. Credits: NASA/JPL-Caltech
Ever since scientists confirmed the existence of seven terrestrial planets orbiting TRAPPIST-1, this system has been a focal point of interest for astronomers. Given its proximity to Earth (just 39.5 light-years light-years away), and the fact that three of its planets orbit within the star’s “Goldilocks Zone“, this system has been an ideal location for learning more about the potential habitability of red dwarf stars systems.
This is especially important since the majority of stars in our galaxy are red dwarfs (aka. M-type dwarf stars). Unfortunately, not all of the research has been reassuring. For example, two recent studies performed by two separate teams from the Harvard-Smithsonian Center for Astrophysics (CfA) indicate that the odds of finding life in this system are less likely than generally thought.
An artist’s conception shows the planet TRAPPIST-1h. (NASA / JPL-Caltech)
The announcement of a seven-planet system around the star TRAPPIST-1 earlier this year set off a flurry of scientific interest. Not only was this one of the largest batches of planets to be discovered around a single star, the fact that all seven were shown to be terrestrial (rocky) in nature was highly encouraging. Even more encouraging was the fact that three of these planets were found to be orbiting with the star’s habitable zone.
Since that time, astronomers have been seeking to learn all they can about this system of planets. Aside from whether or not they have atmospheres, astronomers are also looking to learn more about their orbits and surface conditions. Thanks to the efforts of a University of Washington-led international team of astronomers, we now have an accurate idea of what conditions might be like on its outermost planet – TRAPPIST-1h.
Artist’s impression of the surface of the planet Proxima b orbiting the red dwarf star Proxima Centauri. The double star Alpha Centauri AB is visible to the upper right of Proxima itself. Credit: ESO
The past year has been an exciting time for those engaged in the hunt for extra-solar planets and potentially habitable worlds. In August of 2016, researchers from the European Southern Observatory (ESO) confirmed the existence of the closest exoplanet to Earth (Proxima b) yet discovered. This was followed a few months later (February of 2017) with the announcement of a seven-planet system around TRAPPIST-1.
The discovery of these and other extra-solar planets (and their potential to host life) was an overarching theme at this year’s Breakthrough Discuss conference. Taking place between April 20th and 21st, the conference was hosted by Stanford University’s Department of Physics and sponsored by the Harvard-Smithsonian Center for Astrophysics and Breakthrough Initiatives.
Artist's impression of rocky exoplanets orbiting Gliese 832, a red dwarf star just 16 light-years from Earth. Credit: ESO/M. Kornmesser/N. Risinger (skysurvey.org).
Back in February of 2017, NASA announced the discovery of a seven-planet system orbiting a nearby star. This system, known as TRAPPIST-1, is of particular interest to astronomers because of the nature and orbits of the planets. Not only are all seven planets terrestrial in nature (i.e. rocky), but three of the seven have been confirmed to be within the star’s habitable zone (aka. “Goldilocks Zone”).
But beyond the chance that some of these planets could be inhabited, there is also the possibility that their proximity to each other could allow for life to be transferred between them. That is the possibility that a team of scientists from the University of Chicago sought to address in a new study. In the end, they concluded that bacteria and single-celled organisms could be hopping from planet to planet.
Artist's impression of a system of exoplanets orbiting a low mass, red dwarf star. Credit: NASA/JPL
It turns out that the TRAPPIST-1 star may be a terrible host for the TRAPPIST planets announced in February.
The TRAPPIST-1 star, a Red Dwarf, and its 7 planets caused a big stir in February when it was discovered that 3 of the rocky planets are in the habitable zone. But now more data is coming which suggests that the TRAPPIST-1 star is much too volatile for life to exist on its planets.
Red Dwarfs are much dimmer than our Sun, but they also last much longer. Their lifetimes are measured in trillions of years, not billions. Their long lives make them intriguing targets in the search for habitable worlds. But some types of Red Dwarf stars can be quite unstable when it comes to their magnetism and their flaring.
Our own Sun produces flares, but we are protected by our magnetosphere, and by the distance from the Sun to Earth. Credit: NASA/ Solar Dynamics Observatory,
A new study analyzed the photometric data on TRAPPIST-1 that was obtained by the K2 mission. The study, which is from the Konkoly Observatory and was led by astronomer Krisztián Vida, suggests that TRAPPIST-1 flares too frequently and too powerfully to allow life to form on its planets.
The study identified 42 strong flaring events in 80 days of observation, of which 5 were multi-peaked. The average time between flares was only 28 hours. These flares are caused by stellar magnetism, which causes the star to suddenly release a lot of energy. This energy is mostly in the X-ray or UV range, though the strongest can be seen in white light.
While it’s true that our Sun can flare, things are much different in the TRAPPIST system. The planets in that system are closer to their star than Earth is to the Sun. The most powerful flare observed in this data correlates to the most powerful flare observed on our Sun: the so-called Carrington Event.The Carrington Event happened in 1859. It was an enormously powerful solar storm, in which a coronal mass ejection struck Earth’s magnetosphere, causing auroras as far south as the Caribbean. It caused chaos in telegraph systems around the world, and some telegraph operators received electric shocks.
Earth survived the Carrington Event, but things would be much different on the TRAPPIST worlds. Those planets are much closer to their Sun, and the authors of this study conclude that storms like the Carrington Event are not isolated incidents on TRAPPIST-1. They occur so frequently that they would destroy any stability in the atmosphere, making it extremely difficult for life to develop. In fact, the study suggests that the TRAPPIST-1 storms could be hundreds or thousands of times more powerful than the storms that hit Earth.
A study from 2016 shows that these flares would cause great disturbances in the chemical composition of the atmosphere of the planets subjected to them. The models in that study suggest that it could take 30,000 years for an atmosphere to recover from one of these powerful flares. But with flares happening every 28 hours on TRAPPIST-1, the habitable planets may be doomed.
The Earth’s magnetic field helps protects us from the Sun’s outbursts, but it’s doubtful that the TRAPPIST planets have the same protection. This study suggests that planets like those in the TRAPPIST system would need magnetospheres of tens to hundreds of Gauss, whereas Earth’s magnetosphere is only about 0.5 Gauss. How could the TRAPPIST planets produce a magnetosphere powerful enough to protect their atmosphere?
It’s not looking good for the TRAPPIST planets. The solar storms that hit these worlds are likely just too powerful. Even without these storms, there are other things that may make these planets uninhabitable. They’re still an intriguing target for further study. The James Webb Space Telescope should be able to characterize the atmosphere, if any, around these planets.
Just don’t be disappointed if the James Webb confirms what this study tells us: the TRAPPIST system is a dead, lifeless, grouping of planets around a star that can’t stop flaring.
