Buzz
Isaac Asimov once portrayed the solar system as consisting of the Sun, Jupiter, and cosmic debris. He wasn’t far off—the Sun holds 99.8% of the total mass in our solar system. But what exactly is this fiery giant up there? How does it function, and what mysteries still elude scientists? In 2017, Mytour spoke with astrophysicist and Johns Hopkins University Applied Physics Laboratory's Solar Section Supervisor, Angelos Vourlidas, to uncover what we know about the Sun—and the gaps in our understanding.
1. The Sun acts as a colossal nuclear fusion reactor.
The Sun's size is so staggering that trying to truly visualize it seems almost futile. It's approximately 860,000 miles in diameter, large enough to accommodate 1.3 million Earths. At 4.5 billion years old, it has a long lifespan ahead, with another 6.5 billion years to go. When it nears the end of its life, it won’t explode as a supernova, due to its insufficient mass. Instead, it will expand into a red giant, engulfing Earth in the process (though, by that time, we likely won’t be around), before eventually shrinking into a white dwarf.
The Sun is made up of 74 percent hydrogen and 25 percent helium, with trace amounts of other elements mixed in. Every second, its core undergoes nuclear reactions, fusing hundreds of millions of tons of hydrogen into the same amount of helium, producing the heat and light that we enjoy so much.
2. The Sun follows a galactic-scale orbit.
The Sun does rotate, but not in the same manner as Earth or other terrestrial planets. Like the gas and ice giants, its equator and poles rotate at different speeds. It takes the Sun's equator 24 days to complete one rotation, while its poles take 35 days. In addition, the Sun has its own orbit. Traveling at a speed of 450,000 miles per hour, it orbits the center of the Milky Way galaxy, completing a full revolution every 230 million years.
3. The Sun has surprisingly unusual temperatures.
The Sun's temperature distribution baffles astrophysicists. Its core reaches an intense 27,000,000°F, while its surface is relatively cooler at 10,000°F—hot enough, as NASA points out, to boil diamonds. But here's the strange part: as you move into the upper layers of the Sun’s corona, temperatures soar again, reaching 3,500,000°F. The reason for this oddity remains a mystery.
4. The Sun has its own atmosphere—and Earth is part of it.
If you witnessed the total solar eclipse of 2017, you saw the Sun appear black, surrounded by a glowing white corona. That halo was just a glimpse of the Sun’s much larger atmosphere. In fact, Earth is located *inside* the Sun’s atmosphere. As Angelos Vourlidas explained to Mytour that year, "It essentially stretches out as far as Jupiter." The Sun is a semi-chaotic system. Every century or so, it undergoes a brief ‘sleep,’ during which its activity slows for two or three decades. When it awakens, it becomes much more active and violent. Scientists are still unsure about why this happens. Currently, we’re in one of these quiet periods.
5. The iron in your blood comes from the Sun's siblings.
The Sun doesn’t have a solid core. Instead, at a staggering 27,000,000°F, it’s entirely composed of plasma. "This is where most of the heavier elements, like iron and uranium, are created—at the cores of stars," Vourlidas noted. "When those stars explode, they release these elements into space. Planets are formed from the remnants, and that’s how we end up with iron in our blood and carbon in our cells. They were made in some other star." Not ours, of course, but a star that exploded in our vicinity long before our Sun existed. Other elements like gold, silver, and plutonium were also born from stellar cores. This is what Carl Sagan meant when he said we are children of the stars.
6. The ultimate goal in Sun science is to understand its eruptions.
For astrophysicists studying the Sun, predicting solar storms is the ultimate challenge. During a coronal mass ejection, a billion tons of plasma can be blasted from the Sun at speeds reaching millions of miles per hour. These eruptions carry about 300 petawatts of energy—that's 50,000 times the energy humans use in one year. As the ejected material travels away from the Sun, it expands, and when it reaches Earth, a portion of its energy impacts our planet. These strikes can cause significant disruptions: spacecraft can be damaged, airliners can experience x-ray surges, and the energy grid might be affected—possibly even catastrophically one day. "Our models predict it could happen every 200 years," Vourlidas explained, "but the Sun doesn’t follow our models."
The most recent major strike on Earth is thought to have occurred in 1859. Back then, the telegraph system failed, but the societal impact was minimal due to the lack of widespread electric lighting and the absence of power grids. If a similar catastrophic event were to hit today, however, the effects could be devastating. "It's the most violent phenomenon in our solar system," Vourlidas said. "We need to know when such a massive plasma eruption leaves the Sun, if it will reach Earth, and how strong the impact will be." With this foresight, spacecraft could shut down sensitive instruments, and power grids could be temporarily turned off to minimize damage.
7. Humanity’s first visit to a star is underway with a solar probe.
In 2018, NASA launched the Parker Solar Probe from the Applied Physics Laboratory to 'kiss' the Sun. The probe is traveling to within 4 million miles of our star—the closest any spacecraft has ever come—and will study the corona and the solar wind. Before the probe's launch, Vourlidas noted, "The only way we understood the Sun’s system was by measuring the properties of the solar wind here on Earth and trying to extrapolate that data back to the Sun." The Parker Solar Probe is now gathering data on the solar wind—its speed, density, and magnetic field—across various points in its orbit around the Sun. With this data, scientists hope to develop new models of the solar wind and improve predictions of solar storms and space weather events.
