How Long Is the Solar System's Longest Day? Venus Has the Answer

Data from NASA's Magellan spacecraft and Pioneer Venus Orbiter is used in an undated composite image of the planet Venus. (Handout via Reuters)
Data from NASA's Magellan spacecraft and Pioneer Venus Orbiter is used in an undated composite image of the planet Venus. (Handout via Reuters)
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How Long Is the Solar System's Longest Day? Venus Has the Answer

Data from NASA's Magellan spacecraft and Pioneer Venus Orbiter is used in an undated composite image of the planet Venus. (Handout via Reuters)
Data from NASA's Magellan spacecraft and Pioneer Venus Orbiter is used in an undated composite image of the planet Venus. (Handout via Reuters)

Data obtained by bouncing radio waves off Venus - treating it, as one scientist said, like a giant disco ball - is providing new insight into Earth's closest planetary neighbor, including a precise calculation of the duration of a Venusian day.

The study also measured the tilt of the Venusian axis and size of the planet's core, allowing for a deeper understanding of an enigmatic world sometimes called Earth's “evil twin.”

It was already known that Venus has the longest day - the time the planet takes for a single rotation on its axis - of any planet in our solar system, though there were discrepancies among previous estimates.

The study found that a single Venusian rotation takes 243.0226 Earth days. That means a day lasts longer than a year on Venus, which makes a complete orbit around the sun in 225 Earth days.

The researchers transmitted radio waves toward Venus 21 times from 2006 to 2020 from NASA's Goldstone Antenna in the Mojave Desert of California and studied the radio echo, which provided information on certain planetary traits, at Goldstone and at the Green Bank Observatory in West Virginia.

“Each individual measurement was obtained by treating Venus as a giant disco ball. We illuminated Venus with a giant flashlight, the radar at Goldstone, and observed the reflections as they swept over the surface of the Earth,” said UCLA planetary astronomy professor Jean-Luc Margot, who led the study published in the journal Nature Astronomy.

“Venus is an amazing laboratory for understanding planet formation and evolution, and it's a stone's throw away. There are likely billions of Venus-like planets in the galaxy,” Margot added.

The new data showed that the Venusian planetary core has a diameter of about 4,360 miles (7,000 km), comparable to Earth's core. Previous Venus core estimates had been based on computer modeling rather than observational data.

Its core is almost certainly composed of iron and nickel, though it is unclear whether it is solid or molten, Margot said.

Venus spins on its axis almost upright - meaning it lacks discernable seasons - while Earth has more of a tilt. The study calculated the Venusian tilt at about 2.64 degrees. Earth's is about 23.5 degrees.

Venus, the second planet from the sun, is similar in structure but slightly smaller than Earth, with a diameter of about 7,500 miles (12,000 km). Above its foreboding landscape is a thick and toxic atmosphere that consists primarily of carbon dioxide, with clouds of sulfuric acid droplets. With a runaway greenhouse effect, its surface temperatures reach 880 degrees Fahrenheit (471 degrees Celsius), hot enough to melt lead.

Venus spins from east to west, the opposite direction from all other planets in our solar system but Uranus. In another quirk, its day-night cycle - the time between sunrises as opposed to the length of a single axial spin - takes 117 Earth days because Venus rotates in the direction opposite of its orbital path around the sun.

Venus has received less scientific attention than Mars, Earth's other planetary next-door neighbor, and other solar system destinations.

“I don't think that Venus would be more difficult to understand than other planets if we had adequate data, but there is a deplorable scarcity of data about Venus,” Margot said.

“There have been no NASA missions to Venus in almost 30 years and about a dozen NASA missions to Mars in this time interval,” Margot said, adding that the new findings on how Venus spins could help any future landing attempts.



Iran Envoy: Jareesh is Part of Our Culture, I Prefer It to Mandi

Enayati says regional ties run deep through shared history (Photo: Turki Al-Oqaili)
Enayati says regional ties run deep through shared history (Photo: Turki Al-Oqaili)
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Iran Envoy: Jareesh is Part of Our Culture, I Prefer It to Mandi

Enayati says regional ties run deep through shared history (Photo: Turki Al-Oqaili)
Enayati says regional ties run deep through shared history (Photo: Turki Al-Oqaili)

With a warm smile and a calm tone, Dr. Alireza Enayati, Iran’s ambassador to Saudi Arabia, reflects on nearly two years in Riyadh, describing a personal journey shaped by culture, cuisine, and diplomacy.

“I’ve visited different regions and tasted traditional Saudi dishes,” Enayati told Asharq Al-Awsat in an interview. “Jareesh –a dish made from cracked wheat and cooked with meat, spices, and vegetables– has become my favorite—I choose it over mandi and other dishes on any occasion.”

According to the Iranian envoy, the two countries share more than just geography. “There are many common dishes between Saudi Arabia and Iran,” he said.

But food is only one layer of the ambassador’s experience. Enayati, who has spent over two decades immersed in Middle East diplomacy, sees deep historical ties binding the region’s peoples together.

“I recently read Al-Hadaqi, a novel about Al-Jahiz—Abu Uthman Amr ibn Bahr—and his life between Baghdad, Basra, and Iran. It left me with a strong sense that the relationships among peoples in this region go far back in history,” he said. “Reading it felt like tracing our steps backward to better understand the present.”

“These are not new connections,” he added. “We’re not creating the relationship—we’re nurturing what has always existed. The cultural and civilizational dialogue has never ceased.”

His comments come against the backdrop of a thaw in relations between Tehran and Riyadh, after both sides agreed in March 2023—under Chinese mediation—to restore diplomatic ties following a seven-year rift.

The ambassador pointed to culinary overlaps as another reflection of cultural convergence. “Stews, for example, are common in both countries,” he said. “Jareesh is part of Iranian culture too, as are lamb and camel meat. And as everyone knows, kebab originated in Iran, but it’s also very popular here in the Kingdom.”

Enayati has built his career around the region. “I’ve spent more than 20 years working on regional affairs and never served outside this part of the world,” he said with a smile. “I’m not sure if that’s a strength or a limitation, but my focus has always been here.”

Appointed to Riyadh as part of a diplomatic breakthrough, Enayati said he is proud to represent Iran in Saudi Arabia. “It’s a great honor. I dedicate my efforts to enhancing bilateral ties and supporting regional peace and stability.”

Looking ahead, Enayati hopes to help build stronger cultural bridges—not only between Saudi Arabia and Iran, but across the broader region. “Arabic and Persian cultures both occupy a distinguished place,” he said. “We must deepen mutual understanding between them.”

He concluded with a nod to Tehran’s long-term vision for cooperation with Riyadh. “Iran and Saudi Arabia are both pillars of regional stability,” he said. “This region belongs to its people, and we view our relationship with the Kingdom through that lens.”