Category: 7. Science

Understanding Titan’s planetary boundary layer (PBL) — the lowest region of the atmosphere influenced by surface conditions — remains challenging due to Titan’s thick atmosphere and limited observations.

Previous modeling studies have also produced inconsistent estimates of surface temperature, a critical determinant of PBL behavior, often without clear explanations grounded in surface energy balance.

In this study, we develop a theoretical framework and apply a three-dimensional dry general circulation model (GCM) to investigate how surface thermal inertia influences surface energy balance and temperature variability across diurnal and seasonal timescales. At diurnal timescales, lower thermal inertia surfaces exhibit larger temperature swings and enhanced sensible heat fluxes due to inefficient subsurface heat conduction.

In contrast, at seasonal timescales, surface temperature variations show weak sensitivity to thermal inertia, as atmospheric damping tends to dominate over subsurface conduction. The PBL depth ranges from a few hundred meters to 1,000 m on diurnal timescales, while seasonal maxima reach 2,000–3,000 m, supporting the interpretation from a previous study that the Huygens probe captured the two PBL structures.

Simulated seasonal winds at the Huygens landing site successfully reproduce key observed features, including near-surface retrograde winds and meridional wind reversals within the lowest few kilometers, consistent with Titan’s cross-equatorial Hadley circulation.

Simulations at the planned Dragonfly landing site predict shallower thermal PBLs with broadly similar wind patterns. This work establishes a physically grounded framework for understanding Titan’s surface temperature and boundary layer variability, and offers a unified explanation of Titan’s PBL behavior that provides improved guidance for future missions.

Sooman Han, Juan M. Lora

Comments: 25 pages, 11 figures
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Atmospheric and Oceanic Physics (physics.ao-ph)
Cite as: arXiv:2506.23477 [astro-ph.EP] (or arXiv:2506.23477v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2506.23477
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Submission history
From: Sooman Han
[v1] Mon, 30 Jun 2025 02:46:00 UTC (6,806 KB)
https://arxiv.org/abs/2506.23477
Astrobiology,

The primary scientific objective of this Habitable Worlds Observatory (HWO) Science Case Development Document (SCDD) is to measure planetary rotation rates of transiting exoplanets to determine the structure, composition, circulation, and aerosol properties of their planetary atmospheres.

For this analysis, HWO would obtain spectroscopic phase curves for planets with orbital periods of 5 – 20+ days, to assess tidal locking radius assumptions. Extending phase curve studies out to longer orbital periods than accessible with current and near-future telescopes will enable detailed investigation of atmospheric structure, composition, and circulation for planets that are much cooler than the more highly irradiated planets accessible with JWST phase curve observations (i.e., T_eq < 500 K for HWO versus 1400 K <= T_eq <= 2600 K for JWST).

Broad wavelength coverage extending from the UV to the NIR would capture both reflected light and thermal emission, enabling HWO to conduct comprehensive characterization of planetary atmospheres. UV observations would probe high altitudes, thereby providing valuable insights into atmospheric (dis)equilibrium, aerosol properties, and the effects of photochemical processes on atmospheric composition.

We also discuss the role of polarimetry in the classification of aerosols and the associated role they play in the atmospheric energy budget that directly ties them to the chemistry and circulation structure of the atmosphere.

Hannah R. Wakeford, Laura C. Mayorga, Joanna K. Barstow, Natasha E. Batalha, Ludmila Carone, Sarah L. Casewell, Theodora Karalidi, Tiffany Kataria, Erin M. May, Michiel Min

Comments: Towards the Habitable Worlds Observatory: Visionary Science and Transformational Technology SCDD, to be presented at HWO2025 and submitted to Astronomical Society of the Pacific following community comments. Feedback welcomed
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Instrumentation and Methods for Astrophysics (astro-ph.IM)
Cite as: arXiv:2506.22839 [astro-ph.EP] (or arXiv:2506.22839v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2506.22839
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From: Hannah R Wakeford
[v1] Sat, 28 Jun 2025 10:40:20 UTC (1,037 KB)
https://arxiv.org/abs/2506.22839
Astrobiology,

The motion of snakes has long fascinated humans: they undulate, they sidewind, they crawl, they even fly .

Together with herpetologists, researchers in the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) have discovered and quantified a new type of locomotion in juvenile anacondas.

As adults, these large snakes are better known for their slow, lumbering gait, but the researchers discovered that young anacondas are much more spry — capable of a quick, one-off, skating movement the researchers dubbed the “S-start” due to the shape the snake makes with its body.

A team led by SEAS professor L. Mahadevan , the Lola England de Valpine Professor of Applied Mathematics, Physics and Organismic and Evolutionary Biology in SEAS and the Faculty of Arts and Sciences, is the first to describe this peculiar movement using a mathematical model that quantifies exactly how the snake executes it. The research is published in Nature Physics .

“This movement is the serpentine analog of the moonwalk – a fast, graceful glide that seems to defy common sense,” Mahadevan said. “We used observations to create a mathematical framework, in order to understand under what conditions movements like this are possible, and why they are lost as the snake gets older, heavier, and relatively less strong.”

Study co-author and Missouri herpetologist Bruce Young first noticed several years ago that young anacondas, when gently prodded, displayed what he could only describe as a startle reflex. “This behavior involved not only forming the body into a very characteristic shape, and moving using a gait previously undescribed from snakes, but also moving remarkably fast,” Young said, noting that anacondas are known for their mass and strength, but not for their speed. “It was clear to me that this was something new, involving different biophysics, than what had been described in snakes.”

Young had at this point never met Mahadevan but was a “big fan” of his work – “He has such a mastery of describing and modeling shape and movement” – that Young pitched to Mahadevan a collaborative analysis. The result was the Nature Physics study, co-authored by former Harvard graduate student Nicholas Young and Indian Institute of Technology Bombay researcher Raghu Chelakkot, who developed the computational model to quantify the movement, along with Mattia Gazzola from the University of Illinois.

In their computational analysis, backed up by experiment and observation, the Harvard researchers found that the S-start is present in a “goldilocks” zone of an anaconda’s weight and relative strength. An adult snake is too heavy to execute the movement, while a newborn snake is too strong and tends to either flail upward or unravel. A youthful anaconda has just the right physical attributes to perform the S-start, in which it neither flies off the ground, nor is it overwhelmed by ground friction.

In describing the S-start, Mahadevan’s team helped correct misconceptions about the better-known sidewinding – the continuous, sideways motion snakes use to slide down sandy hills. In their analysis they found that the S-starts are “non-planar,” as in, some segments of the snake are off the ground, almost as if the snake were walking. “We realized that the sidewinding motion is very similar to this S-motion, in that it consists of S-starts that are repeated again and again,” Mahadevan said.

“Perhaps, from an evolutionary point of view, this transient movement was taken up and then repeated, and this became the origin of sidewinding,” Mahadevan said. Overall, the findings seed new insights into how the S-start reflex works in snakes and could serve to inspire new robotic systems or other innovations.

The research was supported by National Science Foundation grants: BioMatter Division of Material Research 1922321, Materials Research Science and Engineering Centers Division of Materials Research 2011754, and Emerging Frontiers of Multidisciplinary Activities 1830901.

Making biofuels is messy, inefficient and expensive. Vast quantities of crops such as maize and soyabeans must be grown, harvested and processed before their energy, accumulated slowly through natural photosynthesis, can be put to use. Nate Ennist of the Institute for Protein Design (IPD) at the University of Washington, in Seattle, thinks that synthetic proteins can boost the rate of return.

WHEN THE first draft of the DNA sequence that makes up the human genome was unveiled in 2000, America’s president at the time, Bill Clinton, announced that humankind was “learning the language with which God created life”. His assessment was a little quick off the mark. For one thing, the full sequence would not be completed until 2022. For another, whereas scientists can use sequencing tools to read DNA, and CRISPR technology to make small edits, actually writing the genomic language has proved trickier.

The Vera Rubin Observatory is about to start a decade-long survey of the night sky. In the process, it will generate hundreds of petabytes of astronomical data. Hidden within that firehose of information will be clues about some of the universe’s deepest mysteries—from dark matter and dark energy to the evolution of galaxies. To help scientists unlock those new celestial tales, the Rubin Observatory’s team had to invent a bespoke way to organise, analyse and share the data. That technology, which will usher in a new, automated era for astronomy, may be one of the observatory’s most important and enduring legacies.

In the second of two episodes, we visit the Rubin Observatory, 2,700m high in the Chilean Andes, to uncover how the telescope’s data travel from the summit to astronomers’ desks around the world. Listen to the first episode here.

Creating new scientific models of plankton is “critical” to understanding the scale of global climate change, a new scientific study has argued, suggesting that all current models used to simulate the influence of plankton on ocean ecosystems are “based on out of date concepts.”

The landmark study led by Plymouth Marine Laboratory’s Professor Kevin Flynn and including the University of Exeter, recognises the crucial role plankton plans in powering the planet by feeding marine life. Simulating what they do through up-to-date modelling is therefore essential to predict what the future may hold for our planet.

Outlining the significance of plankton to Earth, Professor Flynn said: Plankton are mainly microscopic organisms that grow in the ocean (and also in inland waters) that support the base of the food chain.

“No plankton – no fish, no sharks, no whales, no seals, no coral, etc. However, the diversity of the plankton is critical; that biodiversity cannot be best compressed into just a few groups, yet invariably that is what happens in models.”

The researchers argue that plankton models need updating to reflect contemporary knowledge about plankton physiology, diversity, and their roles in ecosystem functioning.

“We’re using simulation tools built on 30 to 50-year-old concepts to understand the most complex and rapidly changing ecosystems on Earth. And that’s a real problem – not just for science, but for policy and for wider society. We need to be sure that models describe the ecophysiology of these organisms in a realistic manner,” said Professor Flynn.

The study warns of serious consequences – from underestimating biodiversity shifts to missing key drivers of marine productivity and carbon cycling.

Using models with over-simplified conceptual cores runs the risk of getting the “right” results for the wrong reasons, giving a false sense of confidence for using such models in projecting into the future.

On July 3, 2025, at 3:54 pm ET, the Earth will officially reach its furthest point from the Sun for this year. This is called aphelion. Our planet’s orbit is very close to a circle, but it is not a circle. It’s an ellipse, so the Earth gets closer and farther from the Sun as it orbits. The closest point, the perihelion, happens around the first few days of January. The next one will be January 3, 2026.

At the aphelion, the distance from the Earth’s center to the Sun’s center is going to be 152,087,738 kilometers (94,502,939 miles). At its closest, Earth is roughly 5.1 million kilometers (about 3.2 million miles) nearer the Sun, which means the planet gets 6.8 percent more solar radiation in January than it will tomorrow.

If we are further away from the Sun, why is it summer?

It is completely accidental that the aphelion and perihelion are so close to the solstices or the beginning of the year. They have nothing to do with seasons either. The seasons are dictated by the tilt of the Earth.

Basically, right now the Northern Hemisphere is pointing towards the Sun, so up here we get summer and the Southern Hemisphere gets winter. In six months, it is the Southern Hemisphere that is pointing towards the Sun, so it experiences summer while it’s winter up north.

There are cyclical processes at work that shift the actual date and time of aphelion and perihelion. It has shifted by around one day every 58 years, and that shift is for good. Smaller variation, plus the need for a leap day, makes a year-on-year variation of a couple of days common.

In the late 19^th century, New Year’s Day was also the perihelion. In the mid-1200s, the solstices would fall on these two special days.

The shape of Earth’s orbit is not fixed

The reason for these changes is the subtle tugging of Jupiter and Saturn on our planet. Over a period of hundreds of thousands of years, the Earth’s orbit goes from mildly elliptical to almost a circle. We are currently getting the Earth at its most circular. This is one of the Milankovitch cycles.

Something fascinating is that while the shape of the orbit changes, due to the gravitational laws, the year’s length doesn’t change. The orbit simply gets more squished, so during spring and autumn, the Earth tends to be closer to the Sun than it currently is.

Still, the orbit affects the seasons in a peculiar way: their length. Seasons, astronomically speaking, are defined by which quadrant in the orbit our planet is passing through. The more circular the orbit, the closer the length of the seasons. Currently, summer in the Northern Hemisphere is 4.66 days longer than winter, and spring is 2.9 days longer than autumn.

The discovery by the Mars rovers of carbonate in sedimentary rock on the Red Planet has enabled planetary scientists to rewind the clock and tell the tale of how Mars’ warmer, watery climate 3.5 billion years ago changed to the barren, dry and cold environment that it is today.

We know that, in the distant past, Mars was warmer than it is today and had liquid water on its surface. We can see evidence for this in the form of ancient river channels, deltas, lakes and even the eroded coastlines of a large sea in the north. Sometime in the past 3.5 billion years, Mars’ atmosphere thinned and its water either froze or was lost to space. The question is, how did that happen?