Space and astronomy news
In recent years, astronomers have developed techniques to measure the metal content of stars with extreme accuracy. With that capability, astronomers have examined sibling stars to see how their metallicity differs. Some of these co-natal stars have pronounced differences in their metallicity.
New research shows that stars engulfing rocky planets are responsible.
Continue reading “Up to a Third of Stars Ate Some of their Planets”
Photosynthesis changed Earth in powerful ways. When photosynthetic organisms appeared, it led to the Great Oxygenation Event. That allowed multicellular life to evolve and resulted in the ozone layer. Life could venture onto land, protected from the Sun’s intense ultraviolet radiation.
But Earth’s photosynthetic organisms evolved under the Sun’s specific illumination. How would plants do under other stars?
Continue reading “Plants Would Still Grow Well Under Alien Skies”
There’s a link between Earth’s ocean salinity and its climate. Salinity can have a dramatic effect on the climate of any Earth-like planet orbiting a Sun-like star. But what about exoplanets around M-dwarfs?
Continue reading “Ocean Salinity Affects Earth’s Climate. How About on Exoplanets?”
The field of exoplanet study continues to grow by leaps and bounds. As of the penning of this article, 5,572 extrasolar planets have been confirmed in 4,150 systems (with another 10,065 candidates awaiting confirmation. Well, buckle up because six more exoplanets have been confirmed around TOI-1136, a Sun-like star located roughly 276 light-years from Earth. This star is less than 700 million years old, making it relatively young compared to our own (4.6 billion years). This system will allow astronomers to observe how systems like our own have evolved with time.
Continue reading “Six Planets Found Orbiting an Extremely Young Star”
Despite the fact that we’ve discovered thousands of them, exoplanets are hard to find. And some types are harder to find than others. Naturally, some of the hardest ones to find are the ones we most want to find. What can we do?
Keep working on it, and that’s what a trio of Chinese scientists are doing.
Continue reading “What’s the Best Way to Find Planets in the Habitable Zone?”
In the search for “potentially-habitable” extrasolar planets, one of the main things scientists look at is stellar activity. Whereas stars like our own, a G-type (G2V) yellow dwarf, are considered stable over time, other classes are variable and prone to flare-ups – particularly M-type red dwarf stars. Even if a star has multiple planets orbiting within its habitable zone (HZ), the tendency to periodically flare could render these planets completely uninhabitable.
According to a new study, stars like our own may not be as stable as previously thought. While observing EK Draconis, a G1.5V yellow dwarf located 110.71 light-years away, an international team of astronomers witnessed a massive coronal mass ejection that dwarfed anything we’ve ever seen in our Solar System. These observations suggest that these ejections can worsen over time, which could be a dire warning for life here on Earth.
Continue reading “A Sun-Like Star Just Blasted out a Flare That Would be Devastating if it Happened Here”
In just nine months (October 31st, 2021), NASA’s long-awaited James Webb Space Telescope (JWST) will finally be launched to space. Once operational, this next-generation observatory will use its powerful infrared imaging capabilities to study all kinds of cosmological phenomena. It will also be essential to the characterization of extrasolar planets and their atmospheres to see if any are habitable.
In anticipation of this, astronomers have been designating exoplanets as viable candidates for follow-up studies. Using data from the Transiting Exoplanet Survey Satellite (TESS), an international team led by MIT researchers discovered four new exoplanets orbiting a Sun-like star about 200 light-years from Earth. This system could be an ideal place for James Webb to spot a habitable planet.
Continue reading “A Sunlike Star Found With Four (No, Five!) Exoplanets Orbiting It”
Six billion Earth-like planets in the Milky Way? If true, that’s astounding. But the number needs some context.
The Milky Way has up 400 billion stars. So even if there are six billion Earth-like planets, they’re still spread far and wide throughout our vast galaxy.
Continue reading “Astronomers Estimate There Are 6 Billion Earth-Like Planets in the Milky Way”
Astronomers have long understood that there is a link between a star’s magnetic activity and the amount of X-rays it emits. When stars are young, they are magnetically active, due to the fact that they undergo rapid rotation. But over time, the stars lose rotational energy and their magnetic fields weaken. Concurrently, their associated X-ray emissions also begin to drop.
Interestingly, this relationship between a star’s magnetic activity and X-ray emissions could be a means for finding potentially-habitable star systems. Hence why an international team led by researchers from Queen’s University Belfast conducted a study where they cataloged the X-ray activity of 24 Sun-like stars. In so doing, they were able to determine just how hospitable these star systems could be to life.
This study, titled “An Improved Age-Activity Relationship for Cool Stars Older than a Gigayear“, recently appeared in the Monthly Notices of the Royal Astronomical Society. Led by Rachel Booth, a PhD student from the Astrophysics Research Center at Queen’s University Belfast, the team used data from NASA’s Chandra X-ray Observatory and the ESA’s XMM-Newton to examine how the X-ray brightness of 24 Sun-like stars changed over time.
To understand how stellar magnetic activity (and hence, X-ray activity) changes over time, astronomers require accurate age assessments for many different stars. This has been difficult in the past, but thanks to mission like NASA’s Kepler Space Observatory and the ESA’s Convection, Rotation and planetary Transits (CoRoT) mission, new and precise age estimates have become available in recent years.
Using these age estimates, Booth and her colleagues relied on data from the Chandra X-ray observatory and the XMM-Newton obervatory to examine 24 nearby stars. These stars were all similar in mass to our Sun (a main sequence G-type yellow dwarf star) and at least 1 billion years of age. From this, they determined that there was a clear link between the star’s age and their X-ray emissions. As they state in their study:
“We find 14 stars with detectable X-ray luminosities and use these to calibrate the age-activity relationship. We find a relationship between stellar X-ray luminosity, normalized by stellar surface area, and age that is steeper than the relationships found for younger stars…”
In short, of the 24 stars in their sample, the team found that 14 had X-ray emissions that were discernible. From these, they were able to calculate the star’s ages and determine that there was a relationship between their longevity and luminosity. Ultimately, this demonstrated that stars like our Sun are likely to emit less high-energy radiation as they exceed 1 billion years in age.
And while the reason for this is not entirely clear, astronomers are currently exploring various possible causes. One possibility is that for older stars, the reduction in spin rate happens more quickly than it does for younger stars. Another possibility is that the X-ray brightness declines more quickly for older, more slowly-rotating stars than it does for younger, faster ones.
Regardless of the cause, the relationship between a star’s age and its X-ray emissions could provide astronomers and exoplanet hunters with another tool for gauging the possible habitability of a system. Wherever a G-type or K-type star is to be found, knowing the age of the star could help place constraints on the potential habitability of any planets that orbit it.
It has been an exciting time for the field of exoplanet studies lately! Last summer, researchers from the European Southern Observatory (ESO) announced the discovery of an Earth-like planet (Proxima b) located in the star system that is the nearest to our own. And just six months ago, an international team of astronomers announced the discovery of seven rocky planets orbiting the nearby star TRAPPIST-1.
But in what could be the most encouraging discovery for those hoping to find a habitable planet beyond Earth, an an international team of astronomers just announced the discovery of four exoplanet candidates in the tau Ceti system. Aside from being close to the Solar System – just 12 light-years away – this find is also encouraging because the planet candidates orbit a star very much like our own!
The study that details these findings – “Color difference makes a difference: four planet candidates around tau Ceti” – recently appeared online and has been accepted for publication in the Astrophysical Journal. Led by researchers from the Center for Astrophysics Research (CAR) at the University of Hertfordshire, the team analyzed tau Ceti using a noise-eliminating model to determine the presence of four Earth-like planets.
This discovery was made possible thanks to ongoing improvements in instrumentation, observation and data-sharing, which are allowing for surveys of ever-increasing sensitivity. As Steven Vogt, a professor of astronomy and astrophysics at UC Santa Cruz and a co-author on the paper, said in a UCSC press release:
“We are now finally crossing a threshold where, through very sophisticated modeling of large combined data sets from multiple independent observers, we can disentangle the noise due to stellar surface activity from the very tiny signals generated by the gravitational tugs from Earth-sized orbiting planets.”
This is the latest in a long-line of surveys of tau Ceti, which has been of interest to astronomers for decades. By 1988, several radial velocity measurements were conducted of the star system that ruled out the possibility of massive planets at Jupiter-like distances. In 2012, astronomers from UC Santa Barabara presented a study that indicated that tau Ceti might be orbited by five exoplanets, two of which were within the star’s habitable zone.
The team behind that study included several members who produced this latest study. At the time, lead author Mikko Tuomi (University of Hertfordshire, a co-author on the most recent one) was leading an effort to develop better data analysis techniques, and used this star as a benchmark case. As Tuomi explained, theses efforts allowed them to rule out two of the signals that has previously been identified as planets:
“We came up with an ingenious way of telling the difference between signals caused by planets and those caused by star’s activity. We realized that we could see how star’s activity differed at different wavelengths and use that information to separate this activity from signals of planets.”
For the sake of this latest study – which was led by Fabo Feng, a member of the CAR – the team relied on data provided by the High Accuracy Radial velocity Planet Searcher (HARPS) spectrograph at the ESO’s La Silla Observatory in Chile, and the High Resolution Echelle Spectrometer (HIRES) instrument at the W. M. Keck Observatory in Mauna Kea, Hawaii.
From this, they were able to create a model that removed “wavelength dependent noise” from radial velocity measurements. After applying this model to surveys made of tau Ceti, they were able to obtain measurements that were sensitive enough to detect variations in the star’s movement as small as 30 cm per second. In the end, they concluded that tau Ceti has a system of no more than four exoplanets.
As Tuomi indicated, after several surveys and attempts to eliminate extraneous noise, astronomers may finally have a clear picture of how many planets tau Ceti has, and of what type. “[N]o matter how we look at the star, there seem to be at least four rocky planets orbiting it,” he said. “We are slowly learning to tell the difference between wobbles caused by planets and those caused by stellar active surface. This enabled us to essentially verify the existence of the two outer, potentially habitable planets in the system.”
They further estimate from their refined measurements that these planets have masses ranging from four Earth-masses (aka. “super-Earths”) to as low as 1.7 Earth masses, making them among the smallest planets ever detected around a nearby sun-like star. But most exciting of all is the fact that that two of these planets (tau Ceti e and f) are located within the star’s habitable zone.
The reason for this is because tau Ceti is a G-type (yellow dwarf) star, which makes it similar to our own Sun – about 0.78 times as massive and half as bright. In contrast, many recently discovered exoplanets – such as Proxima b and the seven planets of TRAPPIST-1 – all orbit M-type (red dwarf) stars. Compared to our Sun, these stars are variable and unstable, increasing their chances of stripping the atmospheres of their respective planets.
In addition, since red dwarfs are much dimmer than our Sun, a rocky planet would have to orbit very closely to them in order to be within their habitable zones. At this kind of distance, the planet would likely be tidally-locked, meaning that one side would constantly be facing towards the sun. This too makes the odds of life emerging on any such planet pretty slim.
Because of this, astronomers have been looking forward to finding more exoplanets around stars that are closer in size, mass and luminosity to our own. But before anyone gets too excited, its important to note these worlds are Super-Earths – with up to four times the mass of Earth. This means that (depending on their density as well) any life that might emerge on these planets would be subject to significantly increased gravity.
In addition, a massive debris disc surrounds the star, which means that these outermost planets are probably subjected to intensive bombardment by asteroids and comets. This not doesn’t exactly bode well for potential life on these planets! Still, this study is very encouraging, and for a number of reasons. Beyond finding strong evidence of exoplanets around a Sun-like star, the measurements that led to their detection are the most sensitive to date.
At the rate that their methods are improving, researchers should be getting to the 10-centimeter-per-second limit in no time at all. This is the level of sensitively required for detecting Earth analogs – aka. the brass ring for exoplanet-hunters. As Feng indicated:
“Our detection of such weak wobbles is a milestone in the search for Earth analogs and the understanding of the Earth’s habitability through comparison with these analogs. We have introduced new methods to remove the noise in the data in order to reveal the weak planetary signals.”
Think of it! In no time at all, exoplanet-hunters could be finding a plethora of planets that are not only very close in size and mass to Earth, but also orbiting within their stars habitable zones. At that point, scientists are sure to dispense with decidedly vague terms like “potentially habitable” and “Earth-like” and begin using terms like “Earth-analog” confidently. No more ambiguity, just the firm conviction that Earth is not unique!
With an estimated 100 billion planets in our galaxy alone, we’re sure to find several Earths out here. One can only hope they have given rise to complex life like our own, and that they are in the mood to chat!