Understanding the Sun - Parker Solar Probe

NASA’s Parker Solar Probe completed its 29th close approach to the Sun on Sept. 4, once again matching its record speed and proximity to the solar surface. During this flyby, the spacecraft aimed its camera at activity and structures near the Sun’s north pole.

After Latest Swing Past Sun, NASA’s Parker Solar Probe Checks in

NASA’s Parker Solar Probe completed its 29th close approach to the Sun on Sept. 4, again matching its record speed and distance from the solar surface. This time, the spacecraft trained its camera on structures and activity near the Sun’s north pole.

The spacecraft transmitted a beacon tone indicating that its systems were operating normally on Sept. 7. Flying around the Sun on a trajectory that limited communications with Earth, Parker had been out of contact and operating autonomously, as planned, for nine days centered around closest approach.

The flyby, which brought Parker to within 3.8 million miles of the Sun at a top speed of 430,000 miles per hour, allowed the spacecraft to race through and sample almost 40% of the solar circumference within one day during this encounter. During this solar encounter, which started Aug. 30 and ended Sept. 9, Parker’s four scientific instrument packages gathered data from inside the Sun’s atmosphere, or corona.

Parker will begin returning detailed spacecraft telemetry on Friday, Sept. 11, with science data transmission set to run from Sunday, Sept. 13 through Sunday, Sept. 27.

The spacecraft’s observations of the solar wind and solar events, such as coronal mass ejections and the aftermaths of flares, are critical to advancing humanity’s understanding of the Sun and the phenomena that drive high-energy space weather events that pose risks to astronauts, satellites, air travel, and even power grids on Earth. Understanding the fundamental physics of space weather enables more reliable forecasts, helping protect astronauts during future deep-space missions to the Moon and Mars.

Parker Solar Probe launched in August 2018. At the time, the Sun was near the minimum of its 11-year activity cycle. In 2024, representatives from NASA, the National Oceanic and Atmospheric Administration, and the international Solar Cycle Prediction Panel announced that the Sun had reached its solar maximum period. Parker’s 29 encounters with the Sun reflect this change over time, sampling the Sun’s atmosphere from quiet to very active periods. Parker Solar Probe will remain in this orbit around the Sun and continue making observations into the declining phase of solar activity.

Overhead view (not to scale) of Parker Solar Probe’s journey through the inner solar system. The gray lines indicate Parker’s path since its launch in 2018; the green oval indicates its current orbit, which brings the spacecraft to within just 3.8 million miles from the solar surface, with a top speed of 430,000 miles per hour. Both the speed and distance are records set during Parker Solar Probe’s close approach to the Sun on Dec. 24, 2024, and matched during seven flybys since, most recently on Sept. 4, 2026.

The Parker Solar Probe mission has been extended into 2029 as a result of the 2026 Heliophysics Senior Review.

Parker Solar Probe was developed as part of NASA’s Living With a Star program to explore aspects of the Sun-Earth system that directly affect life and society. The program is managed by the agency’s Goddard Space Flight Center in Greenbelt, Maryland, for NASA’s Science Mission Directorate in Washington. Johns Hopkins Applied Physics Laboratory (APL) in Laurel, Maryland manages Parker Solar Probe for NASA and designed, built, and operates the mission. 

Source: After Latest Swing Past Sun, NASA’s Parker Solar Probe Checks in

Dark Energy Debunked? A New Look at 1,700 Supernovae Suggests the Universe May Be Slowing Down

For more than two decades, one idea has anchored our picture of the cosmos: the universe isn’t just expanding, it’s speeding up, driven by a mysterious “dark energy” baked into empty space itself. That conclusion won the 2011 Nobel Prize in Physics. Now a new analysis is asking whether it was right all along.

A team led by researchers at the Tata Institute of Fundamental Research in Mumbai, working with Professor Subir Sarkar of the University of Oxford, revisited Pantheon+, one of cosmology’s most important datasets, containing observations of more than 1,700 exploding stars known as Type Ia supernovae. These stellar explosions have long served as cosmic “standard candles,” letting astronomers measure how the universe’s expansion has changed over billions of years.

The twist: the team applied a recently proposed correction that accounts for the age of the stars that produce these supernovae. Once that correction was factored in, the signal for acceleration didn’t just weaken, it flipped. The data pointed toward a universe that is decelerating, not speeding up.

The researchers also tested whether the apparent acceleration looks the same in every direction, an assumption baked into the standard cosmological model. It didn’t. They found the effect was strongest in the direction our local region of space is already moving (as tracked by a hotspot in the cosmic microwave background), and faded with distance. Sarkar argues that’s a problem for dark energy specifically: an effect from the quantum vacuum shouldn’t care which way you’re looking.

Not everyone agrees. In the very same journal issue, a separate team including Oxford’s Professor Maria Vincenzi published a rebuttal defending the standard picture, arguing the evidence for acceleration remains solid and that the debate should now shift to understanding dark energy’s true nature, not questioning its existence.

So who’s right? Neither side has the last word yet. The real test may come from the Rubin Observatory’s Legacy Survey of Space and Time, which is expected to catalogue hundreds of thousands of supernovae in the coming years, a dataset large enough to settle whether the universe’s acceleration is real, directional, or an illusion born from how we measure exploding stars.

Sources

·         Oxford press release: Analysis of supernova data questions evidence for cosmic acceleration

·         Journal article: Sah, Rameez & Sarkar, “Pantheon+ supernovae corrected for progenitor age indicate the universe is decelerating,” Monthly Notices of the Royal Astronomical Society (2026)

 Source: Dark Energy Debunked? A New Look at 1,700 Supernovae Suggests the Universe May Be Slowing Down