Exploring Our Sun Will Help Us Understand Habitability
Scientists have been studying our sun for centuries, and at this point know an awful lot about it — the millions of degrees Fahrenheit heat that it radiates out from the corona, the tangled and essential magnetic fields that it creates, the million-miles-per-hour solar wind and the charged high-energy solar particles that can be so damaging to anything alive.
But we have now entered a time when solar science is taking a major leap forward with the deployment of three pioneering instruments that will explore the Sun and its surroundings as never before. One is a space telescope that will get closer to the Sun (by far) than any probe before, another is a probe that will make the first observations of the Sun’s poles, and the third is a ground-based solar telescope that can resolve the Sun in radically new ways — as seen in the image below, released last month.
The surface of the Sun, with each “kernel” or “cell” roughly the size of Texas. The movie is made up of images produced by the Daniel Inouye SolarTelescope in Hawaii. Novel and even revolutionary data and images are also expected from the Parker Solar Probe (which will travel into the Sun’s atmosphere, or corona) and the just launched Solar Orbiter, which will study (among many other things) the Sun’s polar regions. Credit: NSO/NSF/AURA
Together, NASA’s Parker Solar Probe, the joint European Space Agency-NASA Solar Orbiter mission and the National Science Foundation’s Inouye Solar Telescope on Hawai’i will provide pathways to understand some of the mysteries of the Sun. They include resolving practical issues involving the dynamics of “space weather” that can harm astronauts and telecommunications systems, and larger theoretical unknowns related to all the material that stars scatter into space and onto planets.
Some of those unresolved questions include determining how and why heat and energy flow from the Sun’s inner core to the outer corona and make it so much hotter, determining the structure and dynamics of the plasma and magnetic fields at the sources of the solar wind, the make-up and effects of solar flares and coronal mass ejections, and how and why the Sun is able to create and control the heliosphere — the vast bubble of charged particles blown by the solar wind into interstellar space.
All of this is high-interest science on its own. But it also will provide unparalleled insights into how stars in general behave, and how the radiation and high-energy particles, solar wind and extreme events such as coronal mass ejections emanating from them enables (or much more frequently destroys) the potential habitability of planets that orbit the stars.
I asked Vladimir Airapetian, senior astrophysicist in the Heliophysics Science Division of NASA’s Goddard Space Flight Center and Research Professor at American University, about the potential impact of these new sun-exploring tools on his field and especially on assessing habitability on exoplanets. Airapetian is a team principal investigator in NASA’s Nexus or Exoplanet System Science (NExSS) initiative that brings scientists together to address the question of habitability from a multidisciplinary perspective.
He said the arrival of the three solar observers will have “an enormous impact,” especially in understanding the effects of far less luminous host suns with exoplanets orbiting those suns 20, 30, 40 times closer than in our solar system.
“We don’t know our own sun very well and that limits what we can know about how other stars effect the planets around them…. We can model what energy fluxes a particular star might be sending out to its planets, but those models are limited by the limited data and understanding we have of our sun.”
“These two solar missions plus the most powerful ground-based solar telescope can together revolutionize the field. They will provide data that can and will make sun and exoplanet models so much better. Scientists in heliophysics are very, very excited, and that definitely includes those of us who think about stars and their planets.”
Airapetian has focused on young analog stars in their first 500 million years. It is during this very early phase that the radiation and dramatic events such as flares and coronal mass ejections coming from the star is especially intense, and can permanently make orbiting exoplanets uninhabitable. Or conversely, as Airapetian and colleagues proposed in a Nature Geoscience article in 2016, the solar flares could give a planet sufficient warmth and energy and create the feedstock molecules of life to become habitable.
The Parker Probe and Solar Orbiter in particular have instruments that can collect data on how these high-energy particles are formed and propagated, and their impact on the surrounding heliosphere. This is of special importance when studying the habitability potential of M dwarf stars, which are by far the most common in the galaxy. They are smaller and cooler stars, but start life with extremely powerful superflares of high-energy radiation that can sterilize a planet.
This kind of never-before-collected data from the three new solar missions will also inform an on-going debate about what types of stars are most likely to produce conditions suitable for life on those exoplanets. Is it G-type stars like our own? The ubiquitous — and much “cooler” red dwarf M stars? Or possibly the K-dwarf stars that are now getting a lot of attention and some see as “Goldilocks” suns — not too hot and not too cold for exoplanet life.
With data from Parker Probe, the Solar Orbiter and the Inouye Solar Telescope, this question is expected to be easier to answer,
The first new generation solar explorer to begin operations was the Parker Solar Probe, which launched in 2018 and is now only traveling at 244,255 miles per hour as it speeds around the Sun at a distance of 11.6 million miles from the Sun.
At this point, the Probe will be traveling through a space with temperatures of several million degrees, but the surface of the heat shield that faces the Sun will only get heated to about 2,500 degrees Fahrenheit. Fantastically hot, but using a carbon-carbon heat shield produced by NASA mission partner, the Johns Hopkins University Applied Physics Lab, as well as the physics of temperature and heath, the instrument side of the spacecraft will be at a comfortable 85 F.
(Temperature measures how fast particles are moving, whereas heat measures the total amount of energy that they transfer. Particles may be moving fast — high temperature — but if there are very few of them, they won’t transfer much energy . Since space is mostly empty, there are very few particles that can transfer energy to the spacecraft.)
The Parker probe’s instruments focus on the spacecraft’s immediate surroundings, measuring magnetic fields and particles of plasma, the charged soupy state of matter that makes up the Sun. The primary science goals for the mission are to trace the flow of energy and understand the heating of the solar corona and to explore what accelerates the solar wind. The probe will provide a statistical survey of the outer corona that will enable new understandings of how it behaves. Airapetian said that in the short time the Parker Probe has been in operation and still distant from the Sun, data from the mission has already produced 34 science papers.
The Solar Orbiter, a joint European Space Agency-NASA mission that launched last weekend, will not get nearly as close to the Sun as the Parker Probe. But still, by 2023 it will be making solar pass bys well within the orbit of Mercury.
The main scientific mission is to learn how the Sun creates and controls the heliosphere — the giant bubble of plasma that surrounds the entire solar system and influences the planets within it.
Being so close to the Sun allows for observations of solar surface features and their connection to the heliosphere for much longer periods than from near-Earth vantage points. The view of the solar poles will help us to understand how dynamo processes generate the Sun’s magnetic field.
Nicky Fox, director of heliophysics for NASA, said that science data from Solar Orbitor could be coming in as early as May.
The spacecraft is carrying instruments similar to those found on the Parker Probe. According to Fox, the two will be able to work together to provide a complete picture of the Sun’s processes.
“We waited 60 years to get a spacecraft in the inner heliosphere, and now within 18 months we have two of them up there,” Fox said. “Getting data at the source is already revolutionizing our understanding of our own star and stars across the universe. It’s a great time for heliophysics.”
The National Science Foundation’s (NSF) Daniel K. Inouye Solar Telescope is a four-meter solar telescope the island of Maui, Hawai’i. It’s currently the largest solar telescope in the world. With a focus on understanding the Sun’s explosive behavior, observations of magnetic fields are at the forefront of this innovative telescope.
Valentin Martínez Pillet, director of the National Solar Observatory, which runs the facility, called the Inouye Solar Telescope a microscope on the Sun. “The DKI Solar Telescope will push our understanding of the Sun further than we can imagine,” he said.
The observatory will also measure the wavelengths of light emitted by the Sun and decipher the magnetic signature of light that is under the influence of the Sun’s magnetic field.
And it will produce startling images such as the one at the beginning of this column, which is the highest resolution image of the Sun ever produced.
The Solar Telescope is in the process of going fully online.
These three new platforms will greatly expand knowledge of the Sun and how it allows Earth to be habitable. Given that one star has nurtured life — and has done some for almost 4 billion years — it would be logical to assume that stars like ours would be prime candidates in the search for other potentially habitable worlds. What’s more, G type stars (or “yellow dwarfs”) like our own have much larger habitable zones in which exoplanets might orbit.
But many astronomers and experts in habitability have concluded stars slightly cooler and less luminous than our sun — classified as K dwarfs — are the true “Goldilocks stars,”
As Edward Guinan of Villanova University put it in a release for a American Astronomical Society annual meeting talk last month: “K-dwarf stars are in the ‘sweet spot,’ with properties intermediate between the rarer, more luminous, but shorter-lived solar-type stars (G stars) and the more numerous red dwarf stars (M stars).”
The K stars, especially the warmer ones, have the best of all worlds. If you are looking for planets with habitability, the abundance of K stars pump up your chances of finding life, he said in the release.
These K-stars, also called orange dwarfs, last from 15 billion to 45 billion years. By contrast, our sun, will likely last for but 10 billion years, and is already halfway through its lifetime as a star. Its comparatively rapid rate of stellar evolution will leave the Earth largely uninhabitable in just another 1 or 2 billion years.
The longevity for red dwarf M stars can exceed 100 billion years, but the relative amount of harmful radiation (to life as we know it) that they emit can be 80 to 500 times more intense than from our sun, but only 5 to 25 times more intense for the orange K dwarfs.
So when it comes to distant exoplanets and habitability, host stars are key players. And soon, by studying our sun in new depth and precision, we’ll know a lot more about them.
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The Many Worlds Blog chronicles the search for evidence of life beyond Earth written by author/journalist Marc Kaufman. The “Many Worlds” column is supported by the Lunar Planetary Institute/USRA and informed by NASA’s NExSS initiative, a research coordination network supported by the NASA Astrobiology Program. Any opinions expressed are the author’s alone.