Observing distant objects is no easy task, thanks to our planet’s thick and fluffy atmosphere. As light passes through the upper reaches of our atmosphere, it is refracted and distorted, making it much harder to discern objects at cosmological distances (billions of light years away) and small objects in adjacent star systems like exoplanets. For astronomers, there are only two ways to overcome this problem: send telescopes to space or equip telescopes with mirrors that can adjust to compensate for atmospheric distortion.
Since 1970, NASA and the ESA have launched more than 90 space telescopes into orbit, and 29 of these are still active, so it’s safe to say we’ve got that covered! But in the coming years, a growing number of ground-based telescopes will incorporate adaptive optics (AOs) that will allow them to perform cutting-edge astronomy. This includes the study of exoplanets, which next-generation telescopes will be able to observe directly using coronographs and self-adjusting mirrors. This will allow astronomers to obtain spectra directly from their atmospheres and characterize them to see if they are habitable.
Detecting exoplanets was frontier science not long ago. But now we’ve found over 5,000 of them, and we expect to find them around almost every star. The next step is to characterize these planets more fully in hopes of finding ones that might support life. Directly imaging them will be part of that effort.
But to do that, astronomers need to block out the light from the planets’ stars. That’s challenging in binary star systems.
Researchers at the Australian National University (ANU) are finding new uses for the laser-based technology that sharpens telescope imagery – called adaptive optics – and it just might help mitigate the world’s growing space debris problem. Purpose-built lasers could give derelict satellites a slight ‘push’ of photons, imparting just enough energy to change the debris’s orbit and prevent an impending collision.
Everyone loves lasers. And the only thing better than a bunch of lasers is a bunch of lasers on one of the world’s (soon to be) largest telescopes, the E-ELT. Well, maybe a bunch of lasers on a time-travelling T. Rex that appears in your observatory and demands to know the locations and trajectories of incoming asteroids. That might be better. For the dinosaurs; not for us.
Ever wonder how modern astronomical observatories take such clear images of distant objects? Advances in mirror design have allowed for larger and larger primary mirrors. But adaptive optics play a huge role, too.
Gathering detailed information on exoplanets is extremely difficult. The light from their host star overwhelms the light from the exoplanet, making it difficult for telescopes to see them. But now a team using cutting-edge technology at the Keck Observatory has taken a big leap in exoplanet observation and has detected water in the atmosphere of a planet 179 light years away.
In 2007, the European Southern Observatory (ESO) completed work on the Very Large Telescope (VLT) at the Paranal Observatory in northern Chile. This ground-based telescope is the world’s most advanced optical instrument, consisting of four Unit Telescopes with main mirrors (measuring 8.2 meters in diameter) and four movable 1.8-meter diameter Auxiliary Telescopes.
Recently, the VLT was upgraded with a new instrument known as the Multi Unit Spectroscopic Explorer (MUSE), a panoramic integral-field spectrograph that works at visible wavelengths. Thanks to the new adaptive optics mode that this allows for (known as laser tomography) the VLT was able to recently acquire some images of Neptune, star clusters and other astronomical objects with impeccable clarity.
In astronomy, adaptive optics refers to a technique where instruments are able to compensate for the blurring effect caused by Earth’s atmosphere, which is a serious issue when it comes to ground-based telescopes. Basically, as light passes through our atmosphere, it becomes distorted and causes distant objects to become blurred (which is why stars appear to twinkle when seen with the naked eye).
One solution to this problem is to deploy telescopes into space, where atmospheric disturbance is not an issue. Another is to rely on advanced technology that can artificially correct for the distortions, thus resulting in much clearer images. One such technology is the MUSE instrument, which works with an adaptive optics unit called a GALACSI – a subsystem of the Adaptive Optics Facility (AOF).
The instrument allows for two adaptive optics modes – the Wide Field Mode and the Narrow Field Mode. Whereas the former corrects for the effects of atmospheric turbulence up to one km above the telescope over a comparatively wide field of view, the Narrow Field mode uses laser tomography to correct for almost all of the atmospheric turbulence above the telescope to create much sharper images, but over a smaller region of the sky.
This consists of four lasers that are fixed to the fourth Unit Telescope (UT4) beaming intense orange light into the sky, simulating sodium atoms high in the atmosphere and creating artificial “Laser Guide Stars”. Light from these artificial stars is then used to determine the turbulence in the atmosphere and calculate corrections, which are then sent to the deformable secondary mirror of the UT4 to correct for the distorted light.
Using this Narrow Field Mode, the VLT was able to capture remarkably sharp test images of the planet Neptune, distant star clusters (such as the globular star cluster NGC 6388), and other objects. In so doing, the VLT demonstrated that its UT4 mirror is able to reach the theoretical limit of image sharpness and is no longer limited by the effects of atmospheric distortion.
This essentially means that it is now possible for the VLT to capture images from the ground that are sharper than those taken by the Hubble Space Telescope. The results from UT4 will also help engineers to make similar adaptations to the ESO’s Extremely Large Telescope (ELT), which will also rely on laser tomography to conduct its surveys and accomplish its scientific goals.
These goals include the study of supermassive black holes (SMBHs) at the centers of distant galaxies, jets from young stars, globular clusters, supernovae, the planets and moons of the Solar System, and extra-solar planets. In short, the use of adaptive optics – as tested and confirmed by the VLT’s MUSE – will allow astronomers to use ground-based telescopes to study the properties of astronomical objects in much greater detail than ever before.
In addition, other adaptive optics systems will benefit from work with the Adaptive Optics Facility (AOF) in the coming years. These include the ESO’s GRAAL, a ground layer adaptive optics module that is already being used by the Hawk-I infrared wide-field imager. In a few years, the powerful Enhanced Resolution Imager and Spectrograph (ERIS) instrument will also be added to the VLT.
Between these upgrades and the deployment of next-generation space telescopes in the coming years (like the James Webb Space Telescope, which will be deploying in 2021), astronomers expect to bringing a great deal more of the Universe “into focus”. And what they see is sure to help resolve some long-standing mysteries, and will probably create a whole lot more!
And be sure to enjoy these videos of the images obtained by the VLT of Neptune and NGC 6388, courtesy of the ESO:
Thanks to the deployment of the Kepler mission, thousands of extrasolar planet candidates have been discovered. Using a variety of indirect detection methods, astronomers have detected countless gas giants, super Earths, and other assorted bodies orbiting distant stars. And one terrestrial planet (Proxima b) has even been found lurking in the closest star system to Earth – Proxima Centauri.
As of January 22nd, 2017, some 3,565 exoplanet candidates have been detected in 2,675 planetary systems, and over 2000 of these have been confirmed. However, as already noted, the vast majority of these have been detected by indirect means – generally through the measurement of a star’s radial velocity, or by measuring dips in a star’s luminosity as an exoplanet passes in front of it (i.e. the transit method).
Adaptive Optics, meanwhile, have allowed for the detection of exoplanets directly. When used in astronomy, this technology removes the the effects of atmospheric interference so that light from distant stars or planets can be seen clearly. Relying on experimental technology, the SCExAO was specifically designed and optimized for imaging planets, and is one of several newly-commissioned extreme AO instruments.
However, as Dr. Thayne Currie – a research associate at the NOAJ – indicated, the Observatories on Mauna Kea are particularly well suited to the technology. “Mauna Kea is the best place on this planet to see planets in other stellar systems,” he said. “Now, we finally have an instrument designed to utilize this mountain’s special gifts and the results are breathtaking.”
What makes the SCExAO special is that it allows astronomers the ability to image planets with masses and orbital separations that are similar to those in our own Solar System. So far, about a dozen planets have been detected directly using AO instruments, but these planets have all been gas giants with 4 to 13 times the mass of Jupiter, and which orbit their stars at distances beyond that of Neptune from our Sun.
This improved imaging capacity is made possible by the SCExAO’s ability to compensate for atmospheric interference at a faster rate. This will enable the Subaru Telescope to be able to capture far images of distant stars that are sharper and subject to less glare. And astronomers will be able to discern the presence of fainter objects that are circling these stars – i.e. exoplanets – with greater ease.
The first discovery made with the SCExAO, took place back in October of 2016. At the time, the Subaru telescope had detected a debris disk around HD 36546 – a 2 solar-mass star in the direction of the Taurus constellation – which appeared almost edge on. Located about twice as far from HD 36546 as the Kuiper Belt is from our Sun, this disk is believed to be the youngest debris disk ever observed (3 to 10 million years old).
This test of the SCExAO not only revealed a disk that could be critical to studying the earliest stages of icy planet formation, but demonstrated the extreme sensitivity of the technology. Basically, it allowed the astronomers conducting the study to rule out the existence of any planets in the system, thus concluding that planetary dynamics played no role in sculpting the disk.
More recently, the SCExAO instrument managed to directly detect multiple planets in the system known as HR 8799, which it observed in July of 2016. Prior to this, some of the systems four planets were spotted by surveys conducted using the Keck and the Subaru telescope (before the SCExAO was incorporated). However, these surveys could not correct for all the glare coming from HR 8799, and could only image two of three of the planets as a result.
A follow-up was conducted in the Fall of 2016, combining data from the SCExAO with that obtained by the Coronagraphic High Angular Resolution Imaging Spectrograph (CHARIS). This resulted in even clearer detection of the system’s inner three planets, not to mention high-quality spectrographic data that could allow researchers to determine the chemical compositions of their atmospheres.
As Dr. Olivier Guyon, the head of the SCExAO project, explained, this is a major improvement over other AO surveys. It also presents some major advantages when it comes to exoplanet hunting. “With SCExAO, we know not only the presence of a planet but also its character such as whether it is cloudy and what molecules it has, even if that planet is tens of trillions of miles away.”
Looking at the year ahead, the SCExAO is scheduled to undergo improvements that will allow it to detect planets that are 10 to 10o times fainter than what it can right now. The CHARIS instrument is also scheduled for additional engineering tests to improve its capabilities. These improvements are also expected to be incorporated into next-generation telescopes like the Thirty Meter Telescope – which is currently under construction at Mauna Kea.
For instance, coronagraph are another way astronomers are attempting to refine their search efforts. Consisting of tiny instruments that are fitted inside telescopes, coronagraphs block the incoming light of a star, thus enabling telescopes to spot the faint light being reflected from orbiting planets. When paired with spectrometers, scientists are able to conduct studies of these planet’s atmospheres.
And then you have more ambitious projects like Starshade, a concept currently being developed by Northrop Grumman with the support of NASA’s Jet Propulsion Laboratory. This concept calls for a giant, flower-shaped screen that would be launched with one of NASA’s next-generation space telescopes. Once deployed, it would fly around in front of the telescope in order to obscure the light coming from distant stars.
The era of exoplanet discovery loometh! In the coming decades, we are likely to see an explosion in the number of planets were are able to observe directly. And in so doing, we can expect the number of potentially habitable exoplanets to grow accordingly.
For generations, human beings have fantasized about the possibility of finding extra-terrestrial life. And with our ongoing research efforts to discover new and exciting extrasolar planets (aka. exoplanets) in distant star systems, the possibility of actually visiting one of these worlds has received a real shot in the arm. Unfortunately, given the astronomical distances involved, not to mention the cost of mounting an expedition, doing so presents numerous significant challenges.
However, Russian billionaire Yuri Milner and the Breakthrough Foundation – an international organization committed to exploration and scientific research – is determined to mount an interstellar mission to Alpha Centauri, our closest stellar neighbor, in the coming years. With the backing of such big name sponsors as Mark Zuckerberg and Stephen Hawking, his latest initiative (named “Project Starshot“) aims to send a tiny spacecraft to the Alpha Centauri system to search for planets and signs of life.
Rise above Earth with a telescope, and one huge obstacle to astronomy is removed: the atmosphere. We love breathing that oxygen-nitrogen mix, but it’s sure not fun to peer through it. Ground-based telescopes have to deal with air turbulence and other side effects of the air we need to breathe.
Enter adaptive optics — laser-based systems that can track the distortions in the air and tell computers in powerful telescopes how to flex their mirrors. That sparkling picture above came due to a new system at the Gemini South telescope in Chile.
It’s one of only a handful pictures released, but astronomers are already rolling out the superlatives.
“GeMS sets the new cool in adaptive optics,” stated Tim Davidge, an astronomer at Canada’s Dominion Astrophysical Observatory.
“It opens up all sorts of exciting science possibilities for Gemini, while also demonstrating technology that is essential for the next generation of ground-based mega-telescopes. With GeMS we are entering a radically new, and awesome, era for ground-based optical astronomy.”
Other telescopes have adaptive optics, but the Gemini Multi-Conjugate Adaptive Optics System (GEMS) has some changes to what’s already used.
It uses a technique called “multi-conjugate adaptive optics”. This increases the possible size of sky swaths the telescope can image, while also giving a sharp view across the entire field. According to the observatory, the new system makes Gemini’s eight-meter mirror 10 to 20 times more efficient.
The next step will be seeing what kind of science Gemini can produce from the ground with this laser system. Some possible directions include supernova research, star populations in galaxies outside of the Milky Way, and studying more detail in planetary nebulae — the remnants of low- and medium-mass star.