Why the 7 worlds of TRAPPIST-1 waltz in peculiar patterns

The stability of the TRAPPIST-1 system is the result of a more unstable past. Scientists may have finally revealed the history of the tantalizing TRAPPIST-1 system, an intricate collection of seven worlds that sit about 40 light-years away from us. These worlds, many astronomers and astrobiologists say, may offer us a promising chance of finding life outside the solar system — but they also exhibit peculiar orbital patterns. The newly outlined history of TRAPPIST-1 may, at last, explain how those patterns came to be. When planets form around a young star, their orbital periods often enter "resonances" with each other. An everyday example of a resonance has to do with pushing someone on a playground swing — if you time the push to coincide with the natural frequency of the swing, such as when the swing is just about to go back down, your push would amplify the size of the swing's arc. Similarly, planets often find themselves in resonances with each other. For example, an inner planet can orbit exactly twice for every one orbit of an outer planet. This is a 2:1 resonance, and like pushing a child on a swing amplifies how fast they swing, the exchange of gravitational energy between resonant planets usually makes their orbits unstable, amplifying orbital periods until the planets eventually move out of resonance with one another. Another common planetary resonance is 3:2.

A line-up of the worlds of TRAPPIST-1 are shown in this artist’s impression. (Image credit: NASA/JPL–Caltech)

For the above reason, planetary resonances often become unstable over time, such as in our solar system — but not always. Some planetary systems manage to keep their resonance patterns, and TRAPPIST-1 is one of those systems.

Systems with stable resonances are no doubt aided by how compact the system is; TRAPPIST-1's seven worlds are spread across less than 8 million kilometers, and they would all easily fit inside the orbit of Mercury multiple times over.

TRAPPIST-1's outer three planets — designated f, g and h — are in a chain of 3:2 resonances.

"The outer planets behave properly, so to speak, with the simpler expected resonances," said Gabriele Pichierri, who is a planetary scientist at Caltech, in a statement. "But the inner ones have resonances that are a bit spicier."

For example, the orbital periods of the two innermost planets, b and c, are in an 8:5 resonance, meaning planet b orbits eight times for every five orbits of planet c. Meanwhile, planets c and d are in a 5:3 resonance.

So, how did these complex arrangements arise?

Pichierri is the lead author of a new research paper that delves into the early history of TRAPPIST-1 to discover how its planets wound up in this delicate configuration. The crew found a story of a shifting protoplanetary disk of gas and dust combined with powerful torques that pushed the planets around.

The innermost planets would have formed first, so Pichierri and his team divided the TRAPPIST-1 system into two sub-groups — the inner planets b, c, d and e, and the outer planets f, g and h. (Unlike our solar system, in which the outer planets are gas giants, the outer planets of TRAPPIST-1 are rocky worlds.) Their modeling identified three phases in the evolution of the system.

Here's what the team found.

In the first phase, the four innermost planets all start life in 3:2 resonances with each other, so b and c are in a 3:2 orbital resonance, as are c and d, and d and e. As the inner planets formed out of material from the protoplanetary disk, and their burgeoning red dwarf star ignited nuclear fusion in its core and produced radiation that began to dissipate the disk, the inner edge of the disk would have receded outwards.

In the second phase, planet e, anchored in the receding inner edge of the disk, would have found itself being dragged outwards, away from planets b, c and d and towards the worlds forming in the outer part of the system. This had the effect of causing the orbits of planets b, c and d to waver, and they crossed through the 8:5 and 5:3 resonances as their orbital periods widened, but were then pushed back via a gravitational torque (a twisting, rotational force) from the outer system, until they settled into the 8:5 and 5:3 resonances that they have today.

What of planet e, though? By the final phase, the three outer worlds had formed. Often, when planets form in a protoplanetary disk, they shed orbital angular momentum, exchanging this angular momentum with the disk that they are accreting material from in order to grow. This results in them migrating towards the inner edge of the disk. In the TRAPPIST-1 system, this likely had the effect of pushing planet e back, until the inner and outer parts of the planetary system settled into the configuration that they are in today.

"By looking at TRAPPIST-1, we have been able to test exciting new hypotheses for the evolution of planetary systems," said Pichierri. "TRAPPIST-1 is very interesting because it is so intricate: it’s a long planetary chain, and it’s a great exemplar for testing alternative theories about planetary system formation."

The research was published on Aug. 20 in the journal Nature Astronomy.

Boeing needs to improve quality-control work on SLS moon rocket, NASA Inspector General finds

A scathing report from NASA's Office of Inspector General (OIG) has highlighted several critical issues related to the development of the next version of the agency's Space Launch System megarocket, which will likely delay Artemis moon missions. The report, released by NASA's internal watchdog on Aug. 8, focuses on the gigantic Space Launch System (SLS) Block 1B and its Exploration Upper Stage (EUS). Block 1B is designed to increase the amount of cargo SLS can carry to the moon. The upgraded version is key to NASA's long-term lunar plans and will be used for Artemis 4, currently scheduled to launch in 2028. The OIG found that work being done by Boeing — the prime contractor for the SLS core and upper stages, as well as the rocket's flight avionics suite — at NASA's Michoud Assembly Facility in New Orleans does not meet international standards or agency requirements. This has led to numerous Corrective Action Requests (CARs) issued by the Defense Contract Management Agency (DCMA). A CAR, which can vary in level of severity, indicates that work has not conformed to specific contract requirements.

NASA's Space Launch System rocket launches the Artemis 1 mission, Nov. 16, 2022. (Image credit: Josh Dinner)

According to the OIG report, these quality-control lapses at Michoud are "largely due to the lack of a sufficient number of trained and experienced aerospace workers at Boeing." The report criticizes Boeing's inadequate training and supervision efforts, which fail to mitigate these deficiencies, thereby raising serious concerns about the safety and reliability of the SLS components.

The report also notes growing cost estimates and suggests that Artemis 4 may not hit its expected September 2028 launch date due to such issues.

"We project SLS Block 1B costs will reach approximately $5.7 billion before the system is scheduled to launch in 2028. This is $700 million more than NASA's 2023 Agency Baseline Commitment, which established a cost and schedule baseline at nearly $5 billion," the OIG report states.

"EUS development accounts for more than half of this cost, which we estimate will increase from an initial cost of $962 million in 2017 to nearly $2.8 billion through 2028."

It states that Boeing's delivery of the EUS to NASA has so far been delayed from February 2021 to April 2027. These issues, when combined with other factors, suggest further delays, which would impact Artemis 4.

Boeing's response to these issues has also been found to be ineffective, particularly regarding recurrent quality-control problems.

The OIG's recommendations include developing a compliant quality management training program for Boeing and issuing financial penalties for Boeing's noncompliance with quality standards. A detailed cost overrun analysis on Boeing's EUS development contract is also suggested. NASA agreed with three of four recommendations, but did not agree to institute financial penalties for Boeing's noncompliance with quality-control standards.

The report is another blow to Boeing, whose Starliner spacecraft is currently under scrutiny following its unscheduled, extended stay docked at the International Space Station (ISS) while tests related to problematic reaction control thrusters continue.

It is also another issue for NASA's Artemis program. The Artemis 2 and Artemis 3 missions — the latter being the planned first return of humans to the moon's surface — have this year already been pushed back to September 2025 and September 2026, respectively.

Meanwhile, Artemis' Orion spacecraft, which is built by Lockheed Martin, also faces some trouble. The NASA OIG issued a report in May on Orion heat shield issues, which could further impact the readiness for the Artemis 2 mission, which will send astronauts around the moon.

China’s Space Pioneer pushes towards launch despite static-fire debacle

Chinese commercial launch firm Space Pioneer appears to be moving towards a first launch of its Tianlong-3 rocket despite a disastrous static-fire test in June. Space Pioneer suffered a serious setback in its plans to debut the Tianlong-3 kerosene-liquid oxygen rocket later this year following a static-fire test anomaly June 30. That test saw the first stage escape its test bench and climb into the sky before falling to the ground and exploding. The explosion occurred on a mountainside but was perilously close to inhabited areas, leading to the event being filmed by bystanders. The company was conducting its test as a buildup to an orbital launch of the Tianlong-3, which is benchmarked against the SpaceX Falcon 9. The incident drew widespread attention and no little criticism within China. Space Pioneer initially released a short report on the incident the same day. However, it did not apologize for the event until July 2. Meanwhile, Space Pioneer appears to be proceeding with its plans. Chinese social media posts on July 30 showed a pathfinder article erected at an undisclosed location.

An assembled Tianlong-3 first stage. Credit: Space Pioneer

The test model will be used for integration testing, and procedures required for handling, transporting and erecting a flight rocket.

It is however unclear how Space Pioneer will be able to proceed from this point to an orbital launch attempt. Not only did the company lose its intended flight hardware, but may face regulatory hurdles.

A July 4 post from state media Xinhua on the incident noted that, “the process of climbing to the top of the science and technology industry is not a smooth journey. It is inevitable that there will be setbacks or even failures.” However, a full health check of the commercial sector and assessment and approval processes were mooted.

China opened its space sector to private capital in late 2014 and now boasts around 20 companies focused on launch. Space Pioneer notably became the first Chinese commercial launch company to reach orbit with a liquid propellant rocket with its Tianlong-2 in 2023.

It so far remains unclear if the Space Pioneer incident will significantly slow the company or its competitors. Earlier this year China’s central government designated commercial space as a key industry for support. Reusable medium-lift launchers are also needed to deploy China’s planned low Earth orbit communications megaconstellations.

Competitors Landspace and Deep Blue Aerospace are understood to be preparing for their next vertical takeoff, vertical landing (VTVL) tests. These will be for their respective Zhuque-3 and Nebula-1 orbital rockets.

Landspace is all set to follow up its first, 350-meter-altitude VTVL test, conducted in January, with a higher altitude test in August. The new Zhuque-3 test article appears to include grid fins which were absent on the first hop test.

Deep Blue Aerospace is meanwhile preparing for potentially a full duration first stage flight and recovery test. The company aims to carry out its first orbital Nebula-1 launch before the end of the year. China’s highest altitude hop test so far is 12 kilometers, set by state-owned SAST in June.

The Nebula-1 rocket will initially be capable of carrying 2,000 kilograms to low Earth orbit (LEO). It aims to become China’s first reusable orbital rocket.