Astronomers and backyard enthusiasts work together to detect rare long-period exoplanet

A gas giant the size of Jupiter, yet even heavier and denser, has captured the attention of astronomers across the world. This planet, now confirmed and named TOI-4465 b, lies roughly 400 light-years away, orbiting a star similar to our Sun.

Unlike many other known giant exoplanets, it doesn’t swing close to its star in a tight, fast orbit. Instead, TOI-4465 b takes its time, completing one full orbit every 102 days. That makes it a long-period exoplanet — a rare and scientifically valuable type.

The discovery wasn’t easy. In fact, it all started with a single flicker of light spotted by NASA’s Transiting Exoplanet Survey Satellite (TESS), which catches tiny dips in a star’s brightness when a planet crosses in front of it. That flicker, recorded during one of TESS’s 27-day observation windows, gave scientists a single clue. To confirm the planet, they needed to catch it again — during a very specific 12-hour window, months later.

Postdoctoral Fellow Zahra Essack explained just how tricky it is to spot a single long-period planet transit. “Each transit lasts about 12 hours,” she said, “but it is incredibly rare to get 12 full hours of dark, clear skies in one location.” Weather, telescope time, and geography all limit chances.

But Essack and her team didn’t give up. They rallied researchers around the globe for help. That included not just professionals with access to observatories, but also amateur astronomers. These citizen scientists, spread across 10 countries, turned their personal telescopes toward the sky. In total, 24 of them helped observe the crucial second transit.

Their images and data, taken from locations as far apart as Australia and North America, stitched together the needed proof. The effort worked. The team confirmed the planet’s orbit at about 102 days, capturing its 12-hour transit with global precision. This international effort marked one of the largest citizen-supported discoveries of a long-period planet to date.

TOI-4465 b is no small find. The planet measures 1.25 times the size of Jupiter, making it a true gas giant. But it also has nearly six times Jupiter’s mass and almost three times its density. Scientists measured its density at about 3.73 grams per cubic centimeter — higher than many other known gas giants. That kind of density suggests the planet contains a heavy concentration of metals and rock deep within its layers.

These traits make TOI-4465 b stand out. Most gas giants fall into one of two camps: hot Jupiters, which orbit close to their stars and have very short years, or cold, distant giants like Saturn and Neptune. TOI-4465 b fits neither category. Its orbit is farther out, where temperatures remain moderate — between 375 and 478 Kelvin, or around 200 to 400 degrees Fahrenheit.

Planet structure models suggest that such dense planets likely gained many icy, rocky materials during formation. That fits with the idea that TOI-4465 b formed later in its system’s development, after small solid bodies, known as planetesimals, had already formed.

While the discovery took high-level expertise, it couldn’t have happened without backyard telescopes and shared effort. A few key programs made that collaboration possible.

The TESS Follow-up Observing Program (TFOP), especially its SG1 subgroup, helped organize data from both professionals and amateurs. The Unistellar Citizen Science Network provided tools, training, and software pipelines that made citizen-collected data reliable. The TESS Single Transit Planet Candidate (TSTPC) Working Group, led by Professor Diana Dragomir, helped steer the complex process of verifying a planet from just one fleeting signal.

Essack praised the collaboration. “The Unistellar network provides standardized equipment and data processing pipelines,” she said. “TFOP SG1 offers a global coordination framework that connects professional and amateur astronomers. The TSTPC Working Group brings together the detection and follow-up expertise needed for these challenging observations.”

This infrastructure let citizens contribute real data, handled the same way as images from major observatories. Their role wasn’t symbolic — it was central. “The discovery and confirmation of TOI-4465 b not only expands our knowledge of planets in the far reaches of other star systems,” Essack added, “but also shows how passionate astronomy enthusiasts can play a direct role in frontier scientific research.”

Long-period planets like TOI-4465 b help fill gaps in what we know about planetary systems. Since they move slowly, they don’t transit often, making them hard to detect and even harder to confirm. Most exoplanet discoveries come from short-orbit planets that pass in front of their star many times during short TESS observation periods. Planets with orbits longer than 100 days are often missed or misunderstood.

Essack explained the challenge. “Long-period exoplanets are difficult to detect and confirm due to limited observational opportunities and resources,” she said. “As a result, they are underrepresented in our current catalog of exoplanets.”

Yet these longer orbits match more closely with the conditions found in our own solar system. Earth, for instance, orbits once every 365 days. Studying planets like TOI-4465 b can reveal how systems grow under these cooler, slower-moving conditions. That may help explain why planets form where they do, and how they stay stable over billions of years.

In addition, TOI-4465 b could soon reveal more of its secrets. Its temperature and size make it an excellent target for deeper study using space telescopes like the James Webb Space Telescope (JWST).

Because it doesn’t burn too hot, its atmosphere remains calm enough for spectral study — a method that breaks down the light passing through or reflected from its outer layers. That kind of study can uncover what gases surround the planet, hinting at its history and maybe even signs of habitability in similar worlds.

TOI-4465 b currently ranks among the best long-period planets for emission spectroscopy, a technique used to study what a planet’s atmosphere gives off in heat and light. That opens a door to detailed analysis of its composition and chemistry, something scientists rarely get to do with such distant, slow-orbiting planets.

The discovery of TOI-4465 b reminds scientists not to focus only on the flashy hot Jupiters. While those planets orbit fast and show up often in the data, they don’t represent the full picture. Most planets — especially those more like Earth — live in cooler, wider orbits. To understand those planets, astronomers need to find and study more worlds like TOI-4465 b.

That means keeping an eye out for single-transit events, and being ready to jump into action when one appears. Thanks to TESS and its global support network, teams now have tools to do just that — combining space telescopes, observatories, and the telescopes in backyards.

As the science of exoplanets continues to grow, long-period discoveries like TOI-4465 b will help reshape how we think about distant solar systems. They may be harder to spot, but their slow paths hold deep insights. The stars won’t always give second chances. But when they do, teams like this — spread across continents and connected by shared purpose — are ready to catch them.

Research findings are available online in The Astronomical Journal.

Note: The article above provided above by The Brighter Side of News.

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