Suspected Second-generation Planet Solves NASA Hubble Cold Case

This artist’s concept depicts a possible explanation for the unusual chemical abundances NASA’s Hubble Space Telescope detected in the HS 0209+0832 system: a second-generation planet orbiting a white dwarf star.

Credits: Artwork: NASA, ESA, Leah Hustak (STScI) 

Diligent sleuthing by astronomers has broken open a cold case in the data archive of NASA’s Hubble Space Telescope. In a study published Monday in Nature Astronomy, researchers report uncovering a surprising chemical clue that indicates the white dwarf star HS 0209+0832 may host a second-generation planet. 

A white dwarf is the remnant core of a low-mass star that has burned through all its nuclear fuel and lost its outer envelope of gas and dust to space. A second-generation planet is a world that forms around the stellar remnant from its cast-off material. 

“Rather than the white dwarf stage being a kind of epilogue to the story of a star and its planets, this research points to the systems we are familiar with only being the first chapter of a potentially much longer tale, with some new characters showing up. That’s a really exciting prospect to pursue,” said Jamie Williams, astronomer and lead author, a doctoral candidate at the University of Warwick in the United Kingdom.

Earth and the other planets in our solar system are first-generation planets, which form from material left over from a star’s birth. 

This artist’s concept, not to scale, imagines the evolution of a Sun-like star (1) into an aging red giant (2) and then a small, bright white dwarf surrounded by a disk of its expelled outer layers (3), from which a second-generation planet forms (4). 

Illustration: NASA, ESA, Leah Hustak (STScI)

“What Hubble is showing us in this white dwarf system is something we haven’t seen before: a high abundance of the element niobium, the signature of which I was unfamiliar with when I first found it in the archival data,” Williams said.

When Hubble first observed the star in 1999, the data contained roughly 100 chemical features that could not be identified. Williams went back to those records armed with an updated chemical database and found that niobium matched many of the mystery features.

Williams explained that, while niobium is found in our solar system and has multiple uses on Earth, including in jewelry and medical imaging devices, the amount Hubble found in the HS 0209+0832 system points to a planet forming not from a star’s birth, but from the material ejected as it dies. 

"Niobium and other elements heavier than iron are astronomically special because, unlike many common elements, they are not formed in the cores of stars by thermonuclear fusion,” said Nicholas Stone, a theoretical astrophysicist at the University of Wisconsin – Madison and member of the research team. “Instead, these heavy elements can only be synthesized in the exotic conditions that briefly emerge inside dying stars. The presence of niobium is a signpost of these ‘death’ throes, and the expulsion of the dying star's innards into space.” 

Once the star ejected this chemically enriched material, the team theorizes that some of it coalesced into a gas giant planet. The remainder of the ejecta dispersed long ago, but the planet remains.

“When Jamie asked me about niobium in relation to this study I was truly gobsmacked, as that element had not been reported in any other white dwarf analyzed to date. Once we realized it was there, everything fell into place,” said astronomer and study co-author Boris Gaensicke, also at the University of Warwick.

NASA’s Hubble Space Telescope spectrum shows the unusual abundances of certain elements it found in the HS 0209+0832 system. Dips indicate where niobium, nickel, and calcium are absorbing light, so less light in that part of the spectrum reached Hubble. 

Illustration: NASA, ESA, Leah Hustak (STScI)

The research team confirmed the Hubble observations with data from NASA's retired FUSE (Far Ultraviolet Spectroscopic Explorer) mission, which also showed strong signatures of niobium in the HS 0209+0832 system. 

NASA’s TESS (Transiting Exoplanet Survey Satellite) also observed the white dwarf for four months, allowing it to detect periodic brightness variations that indicate that a planet orbits at a distance of about 3.7 million miles (6 million kilometers), much closer than Mercury orbits the Sun. 

The research team estimates the candidate planet is a gas giant about the size of Jupiter that is rapidly losing atmosphere. Because the white dwarf star is relatively new, it is still very hot and likely blasting this planet with energy that is stripping its outer material. This could result in the planet having a comet-like tail of material that would form a disk around the white dwarf star and fall back on to its surface, leading to Hubble detecting the niobium when studying the star. Despite this mass loss, Williams said that the planet is likely not a temporary blip on the cosmic radar. 

“If the second-generation planet is there, I think it is likely to survive. Eventually the white dwarf will cool and then maintain a consistent temperature, with the planet in its stable habitable zone for millions of years,” Williams said.

Williams added that there is still a lot of work to do to understand these types of systems — how second-generation planets form, how common or rare they are, and how they evolve in orbit around a “dead” star. He’ll use Hubble to explore these questions for the next several years, hoping to build up substantial data and statistics about these new types of celestial bodies.

“I think this research is an important example of the fact that scientific discovery is not a straight path,” Gaensicke said. “It often needs that magical moment when people discuss big questions on their minds and realize that together they can find unexpected answers.”

The Hubble Space Telescope has been operating for more than three decades and continues to make ground-breaking discoveries that shape our fundamental understanding of the universe. Hubble is a project of international cooperation between NASA and ESA (European Space Agency). NASA’s Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope and mission operations. Lockheed Martin Space also supports mission operations at Goddard. The Space Telescope Science Institute in Baltimore, which is operated by the Association of Universities for Research in Astronomy, conducts Hubble science operations for NASA.

Source: Suspected Second-generation Planet Solves NASA Hubble Cold Case - NASA Science

Can Old Knees Regrow Their Cartilage? Blocking an Aging Enzyme Says Maybe

Cartilage has a reputation: once it’s worn down, it stays worn down. That smooth, slippery cushion at the ends of your bones has almost no ability to repair itself, which is why osteoarthritis is so stubborn and why, for many people, the final answer is a knee or hip replacement. A new study from Stanford Medicine, published in Science, suggests that reputation may be a little less deserved than we thought.

The problem: a disease with no real drug

Osteoarthritis is a degenerative joint disease in which cartilage gradually breaks down, leaving joints painful, swollen and stiff. In the United States it affects roughly one in five adults and costs an estimated $65 billion a year in direct health care. Today’s treatments mostly manage symptoms. There is currently no drug that reliably slows or reverses the disease itself.

The damage follows a familiar loop. Under stress from aging, injury or excess weight, the cartilage cells (chondrocytes) start releasing inflammatory molecules and chewing through collagen, the structural protein that gives cartilage its strength. The tissue thins and softens, inflammation adds swelling and pain, and with very little repair capacity, the joint slowly loses.

The suspect: a “gerozyme” called 15-PGDH

The team, led by Helen Blau and Nidhi Bhutani, has spent years studying an enzyme named 15-PGDH. They call it a gerozyme: an enzyme that becomes more abundant with age and contributes to the gradual decline of tissues. Its job is to break down prostaglandin E2, a signaling molecule involved in tissue repair.

Earlier work from the group showed that blocking 15-PGDH boosted muscle mass and endurance in old mice, while raising it in young mice made muscles shrink and weaken. Inhibiting it has also supported regeneration in nerve, bone, colon, liver and blood cells. The obvious next question: what about cartilage?

What they found in mice

First, the correlation: levels of 15-PGDH in knee cartilage roughly doubled between young and old mice. Then came the intervention. The researchers gave older mice a small-molecule inhibitor of the enzyme, either by injection into the abdomen (so it acted body-wide) or directly into the knee joint. Both routes worked. Cartilage that had been thin and poorly functioning became thicker across the joint surface, and importantly it was hyaline cartilage, the smooth, low-friction kind a healthy joint needs, rather than the tougher but less suitable fibrocartilage.

They also tested the drug in a model resembling an ACL tear. About half of people who suffer this common sports injury develop osteoarthritis in that joint within roughly 15 years. In the mice, treatment given twice a week for four weeks after injury sharply lowered the chance of developing osteoarthritis. Untreated animals, whose 15-PGDH levels had doubled after injury, developed the disease within four weeks. The treated mice also walked more normally and put more weight on the injured leg.

The twist: it’s not stem cells

Most regeneration stories involve stem cells multiplying and maturing into new tissue. The researchers expected the same here, but cartilage didn’t follow the script. Instead, the existing chondrocytes changed their gene activity and shifted toward a more youthful state.

Looking at cell populations in old mice, the shifts were striking:

·         Cells making 15-PGDH and expressing cartilage-degrading genes fell from 8% to 3%.

·         Cells expressing fibrocartilage-forming genes fell from 16% to 8%.

·         Cells expressing genes for hyaline cartilage and a healthy extracellular matrix rose from 22% to 42%.

In other words, the treatment nudged a large pool of cells already sitting in the joint toward a repair-friendly program. As Blau put it, they were looking for stem cells, and they were clearly not involved.

Human cartilage responded too

The team also tested cartilage removed from people with osteoarthritis during total knee replacement surgery. After one week of exposure to the inhibitor, the tissue had fewer 15-PGDH-producing chondrocytes, lower activity of degradation and fibrocartilage genes, and began regenerating articular cartilage.

Before we cancel the joint replacements

Headlines asking whether this means “goodbye joint replacements” are getting ahead of the data. A few honest caveats:

·         The strongest results are in mice. The human data come from tissue samples in the lab, not from patients receiving a drug.

·         The study does not yet show that the approach regrows cartilage or prevents osteoarthritis in people. That needs clinical trials testing safety and effectiveness specifically for cartilage.

·         There is a promising head start: an oral 15-PGDH inhibitor has already completed Phase 1 testing for age-related muscle weakness, where it was reported to be safe and active in healthy volunteers. The researchers hope a cartilage trial follows soon.

·         Disclosure worth noting: Blau, Bhutani and other co-authors are inventors on Stanford patent applications covering 15-PGDH inhibition for cartilage and tissue rejuvenation, licensed to Epirium Bio. Blau is a cofounder of Myoforte/Epirium and holds equity in the company.

Why it matters

Even with those caveats, the conceptual shift is the real headline. If aging cartilage can be coaxed back toward a younger state by turning down one enzyme, then “damaged beyond repair” may sometimes mean “repair switched off.” A pill or injection that restarts that repair could one day change how we treat arthritis, and how we protect knees after sports injuries, long before surgery becomes the only option. We’re not there yet, but it’s a very interesting place to be heading.

Sources

·         Press release: Stanford Medicine, “Blocking a ‘gerozyme’ reverses cartilage loss in mice”

·         Original paper: Singla M, Wang YX, Monti E, et al., Blau HM, Bhutani N. “Inhibition of 15-hydroxy prostaglandin dehydrogenase promotes cartilage regeneration.” Science 2026; 391(6789):1053. DOI: 10.1126/science.adx6649

Source: Can Old Knees Regrow Their Cartilage? Blocking an Aging Enzyme Says Maybe