{"id":"a7618aef-8b65-4103-85d5-a17a4a56b211","arxiv_id":"2504.20663","paper_version":1,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":7.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":2,"one_line_summary":"Using Solar Orbiter EUI images, the authors report 27 small-scale jets in an erupting solar filament with speeds up to about 800 km/s, the fastest nanojet-like events observed to date.","lead":"Solar Orbiter EUI images captured 27 tiny plasma jets in an erupting solar filament, moving at up to 800 km/s. These are the fastest small-scale jets seen in the solar atmosphere, suggesting nanoflare-type reconnection can release energy more violently than thought.","discovery_kind":"new_application","skeptic_critique":{"model":"deepseek-v4-flash","headline":"Untwisting of the erupting filament, not reconnection outflows, may explain the reported ~800 km/s apparent speeds; the paper never measures the untwisting rate to exclude this.","rationale":"The reader identified the same weak point: the apparent vs. real nature of the tracked fronts. My stress-test agrees and sharpens it into a quantitative alternative: the untwisting of the filament, which the paper explicitly acknowledges, can generate apparent transverse motions along a fixed slit at speeds comparable to those reported. Because the paper's central novelty—the unprecedentedly high speeds—depends entirely on interpreting the time-distance slopes as bulk reconnection outflows, and because the paper presents no measurement of the untwisting rate and no test of the scaling of velocity with radius, the claim is not currently supported. The proposed check is feasible with the same EUI data and would either rule out the dominant pattern-motion alternative or force a reinterpretation. I therefore keep the reader's CONDITIONAL verdict: the work is plausible and interesting, but acceptance should require this quantitative exclusion of the untwisting interpretation. I do not see an internal inconsistency or a fatal error; the concern is an unaddressed but addressable ambiguity.","tokens_in":11537,"tokens_out":10693,"duration_ms":114304,"concrete_test":"Using the same EUI 2-s cadence images, track the apparent rotation of the filament threads in the region of Figure 2 over the 7-minute eruption (e.g., by cross-correlating consecutive frames or by following the motion of individual thread brightenings) to obtain the angular velocity ω(t) and its uncertainty. For each of the 27 events, compute the expected apparent transverse speed v_r = ω r, where r is the perpendicular distance from the filament spine at the event location. If the measured speeds are systematically much larger than v_r (e.g., by more than a factor of two for a majority of events) and do not increase with r, then the untwisting pattern-motion interpretation is excluded; if v_r is comparable to the measured speeds, the reported 'nanojet' velocities should be reinterpreted as rotation-induced pattern speeds, not reconnection outflows.","verdict_should_be":"UNCHANGED","load_bearing_attack":"Section 3 measures nanojet speeds from the slopes of bright fronts in time-distance maps (Figure 2c) and interprets them as bulk plasma ejections from component reconnection, leading to the claim of unprecedented speeds (~800 km/s). The same section states that the filament is untwisting, and the time-distance map in Figure 2b shows this motion. A rotating filament thread crossing a fixed slit produces an apparent transverse displacement along the slit at speed v = ω r, where ω is the angular velocity of the untwisting and r is the distance of the thread from the filament axis. To produce the 770 km/s of event No. 13 from a radius of r ≈ 5 Mm requires ω ≈ 0.15 rad/s, i.e., a full revolution in ~40 s. The paper does not measure ω, does not test whether the observed speeds scale with r, and does not argue that the untwisting is too slow. The near-symmetric distribution of events toward the upper right (14) and lower left (13) is equally consistent with the two sides of a rotating structure. With a single EUI viewpoint and no simultaneous spectroscopic or stereoscopic data, the apparent motions could also be a propagating heating or compression front rather than plasma flow. The kinetic-energy estimate in Section 3 assumes the motion is bulk flow, so the energy and magnetic-field values are not meaningful if the fronts are pattern motions. The 'highest speeds ever' claim therefore rests on an untested and easily testable assumption.","agreement_with_reader":"agree"},"referee_report":{"model":"deepseek-v4-flash","summary":"The paper reports Solar Orbiter/EUI 174 Å observations of 27 small-scale jet-like events ('nanojets') in an erupting filament on 2024 September 30. Speeds are measured from time–distance maps and, for the shortest events, by manual front tracking between adjacent frames; the reported range is 128–770 km s⁻¹, with the fastest event (No. 13) described as approximately 800 km s⁻¹ in the abstract. The authors interpret the features as component-reconnection outflows perpendicular to the untwisting filament threads, estimate kinetic and thermal energies of 10²²–10²⁵ erg using assumed density and temperature, and claim these are the highest speeds ever reported for sub-Mm solar jets. The paper explicitly acknowledges that the speeds are plane-of-sky lower limits and that density and temperature are assumed rather than measured.","tokens_in":11739,"tokens_out":5328,"duration_ms":56029,"significance":"If the interpretation is correct, the result is significant: it would demonstrate that component magnetic reconnection can drive sub-Mm plasma ejections at speeds comparable to the coronal Alfvén speed, with direct implications for nanoflare heating and reconnection physics. The use of 2 s cadence EUI data is a genuine observational advance, and the paper is honest about projection effects, dynamic blurring, and assumed plasma parameters. The slope-based measurement for the longest event (Table 1, No. 13, Figure 2) is straightforward, and the table of all 27 events is useful. However, the central 'unprecedented speeds' claim rests on the assumption that the tracked bright fronts are bulk plasma ejections rather than apparent pattern motion from the untwisting filament; this assumption is neither quantitatively tested nor excluded. The lack of error bars on the catalog further weakens the quantitative comparison with previous work.","major_comments":[{"comment":"The central speed claim is not uniquely established because the tracked bright fronts may be apparent pattern motion from the untwisting filament rather than bulk plasma ejections. The time–distance map in Figure 2b shows the untwisting motion, and the paper does not measure the angular velocity ω of the untwisting or test whether the observed speeds are consistent with v = ωr for threads at distance r from the filament axis. For event No. 13, v = 770 km s⁻¹ at r ≈ 5 Mm would require ω ≈ 0.15 rad s⁻¹ (a full revolution in ~40 s), which the paper does not argue to be impossible. With a single EUI viewpoint and no simultaneous spectroscopy or stereoscopy, a propagating heating/compression front or a rotating-thread pattern cannot be excluded. I request either a quantitative exclusion of this alternative (for example, by measuring ω from the time–distance data and checking the predicted scaling of speed with r, or by comparing the intensity evolution of the fronts with a pure pattern-motion prediction) or a substantial softening of the 'highest speeds ever reported' claim.","section":"Section 3, Figure 2, Table 1"},{"comment":"The catalog lacks error bars, and for the 18 events with durations of 2–4 s (i.e., one or two frames at the 2 s cadence) the speeds are estimated by manual front tracking between adjacent frames, as stated in Section 3. With a pixel size of 0.105 Mm and a 2 s cadence, a one-pixel displacement error corresponds to about 50 km s⁻¹, and the systematic uncertainty from ambiguous front identification is likely larger; the 1.65 s exposure time further smears the front position. The paper should provide uncertainty estimates for each speed, or at least for the highest-speed events, and discuss how the exposure time affects the measured front positions. Without this, the statement that 22 out of 27 events exceed 300 km s⁻¹ is not quantitatively supported.","section":"Table 1 and Section 3"},{"comment":"The kinetic and thermal energy estimates rest on assumed values of the electron density n_e = 10⁹ cm⁻³ and temperature T = 2 MK, and the derived magnetic field B ≈ 20 G follows directly from equating the total estimated energy to B²V/8π. The authors themselves note that dynamic blurring may make the apparent length (and hence volume and energy) too large by a factor of about two, so the energy values in Table 1 should be presented as order-of-magnitude illustrations rather than as measured quantities. This does not affect the speed measurement itself, but it weakens the nanoflare-classification argument if a reader relies on the stated energies and the derived field strength.","section":"Section 3, Eq. (1)"}],"minor_comments":[{"comment":"The sentence 'Detection and investigation of nanojets are are hampered' contains a duplicated 'are'.","section":"Introduction"},{"comment":"The sentence 'using SkyCoord.transform to from the astropy.coordinates module' contains a stray 'to'.","section":"Section 2"},{"comment":"The word 'Previouly' should be 'Previously'.","section":"Section 4"},{"comment":"The horizontal axis of the speed panel appears to read 'peed( m s)' and should be 'Speed (km s⁻¹)'.","section":"Figure 4"},{"comment":"The in-text citation 'Ryan et al. 2025, submitted' does not appear in the reference list; a full citation or a note on its status is needed.","section":"References"},{"comment":"Several numerical entries contain spurious spaces (e.g., '9 .23 × 1022'); the table formatting should be cleaned for publication.","section":"Table 1"}],"recommendation":"major_revision","confidential_remarks":null},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Colleague,\n\nWhat you should know: this is a genuinely new observation — first report of nanojets in an erupting, untwisting filament, using EUI 174A at 2 s cadence. The speeds clearly exceed the prior 50–300 km/s range, with the fastest event (No. 13) showing a clean, monotonic 28 s streak in a time-distance map at 770 km/s. That single event is hard to dismiss on cadence grounds. The paper also does some things right: it flags plane-of-sky projection, discusses dynamic blurring and corrects energy estimates downward, and explicitly lists its limitations. The catalog is small but the raw data exist for others to check.\n\nThe soft spot is the interpretation. The stress-test concern lands: the paper never measures the untwisting rate of the filament, so the possibility that some of these bright fronts are apparent motions from a rotating thread crossing the slit is not excluded. For the 2–4 s events, that's a real risk; a few frames of apparent motion can easily masquerade as a fast jet. The symmetric direction distribution (14 upper-right, 13 lower-left) is exactly what you'd expect from either symmetric reconnection outflows or the two sides of a rotating structure. For the 28 s event, the slope is monotonic and nearly straight, which is less naturally produced by a ~40 s-period rotation, but the paper never computes the angular velocity, so the alternative isn't actually tested. This is the load-bearing issue for the 'unprecedented' claim, and it is fixable with the existing data: measure the untwisting angular speed, check whether apparent speeds scale with distance from the filament axis, and show that the brightest streak is not a projection of the rotating thread.\n\nMinor points: the catalog lacks error bars, and the shortest events are manually tracked at the cadence limit. The energy estimates rely on assumed density and temperature, and the derived 20 G field is order-of-magnitude only; fine as rough numbers, but not constraints. The citation pattern is fine — self-citations are contextual and prior speed values are assembled fairly.\n\nWho is this for? Solar physicists working on coronal heating, reconnection, and high-resolution EUI observations. It deserves a serious referee — the observation is novel and the data can answer the key question — but the revision needs the untwisting check, error bars, and a clearer selection procedure. I'd send it to review, expecting heavy revision. My own verdict: interesting and probably real, but not yet proven.","headline":"Novel EUI nanojet speeds are real enough to warrant review, but the paper must rule out untwisting-induced apparent motions before the 'unprecedented' claim can stand.","tokens_in":12381,"tokens_out":2527,"would_cite":true,"duration_ms":27403,"reading_group":"yes","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":[],"model":"deepseek-v4-flash","headline":"Using 2-second extreme-ultraviolet images, this paper reports 27 nanojets in an erupting filament with speeds up to about 800 km/s, the fastest ever seen for small-scale solar jets.","keywords":["The Sun","solar corona","solar magnetic reconnection","solar filament eruptions","nanojets","component reconnection","coronal heating","EUV imaging"],"falsifier":"A decisive test would be a coordinated observation of the same erupting filament from a second high-resolution EUV viewpoint, reconstructing the three-dimensional motion of one of the tracked fronts to check whether its true velocity is a radial ejection near 800 km/s. Failing that, a calculation of the apparent speed produced by the filament's untwisting, using the observed rotation and geometry, could show whether the time–distance slopes are compatible with pattern motion alone; if they are, the nanojet speeds would be overestimated.","tokens_in":11277,"feed_emoji":"☀️","tokens_out":11200,"duration_ms":104390,"temperature":0.7,"pith_summary":"The paper reports 27 small, short-lived plasma jets—nanojets—inside an erupting solar filament, seen in 2-second-cadence extreme-ultraviolet images from the Solar Orbiter EUI telescope. Most of the jets move at about 450 km/s and the fastest at roughly 800 km/s, which the authors state are the highest speeds ever reported for small-scale jets less than about 1 Mm wide on the Sun. The speeds matter because nanojets are considered direct markers of nanoflare heating, the leading explanation for why the corona is millions of degrees hotter than the visible surface. If the measurement is right, component magnetic reconnection can fling sub-Mm plasma ejections at speeds comparable to the coronal Alfvén speed, making nanoflare-type energy release far more violent than earlier detections suggested.","feed_headline":"Small solar jets hit 800 km/s","feed_subtitle":"New EUI observations catch sub-Mm reconnection jets far faster than earlier nanojet sightings.","key_machinery":"The load-bearing measurement is the time–distance map: a slit drawn along each jet's ejection direction in the EUI 174 Å images, with the slope of the bright front's trajectory giving the plane-of-sky speed. The interpretation rests on component reconnection, the slingshot mechanism in which two magnetic field lines with a small misalignment angle reconnect and eject plasma perpendicular to the field; the simulations cited in the paper predict exactly such collimated ejections. Supporting steps include Gaussian fits to intensity profiles for jet width, an assumed coronal electron density of $10^9\\ \\mathrm{cm}^{-3}$ to convert volumes into kinetic energies, and an estimate of motion blur over the 1.65 s exposure. The untwisting filament threads are presented as the source of the misalignment angles.","core_discovery":"During the untwisting of a filament in an active region on 2024 September 30, the authors identify 27 jet-like features oriented roughly perpendicular to the filament's spine. Tracking bright fronts in EUI 174 Å time–distance maps gives plane-of-sky speeds from 128 to 770 km/s, with the fastest event lasting about 28 seconds, spanning about 6.6 Mm in length and 0.7 Mm in width. They classify these as component-reconnection nanojets because their morphology matches previously reported nanojets, their estimated energies ($10^{22}$–$10^{25}$ erg) fall in the nanoflare range, and the untwisting of the filament is argued to create the misalignment angles that trigger component reconnection. The central claim is that these are genuine nanojets whose speeds, up to roughly 800 km/s, are comparable to the coronal Alfvén speed and far above the 50–300 km/s span of earlier nanojet studies; the paper is explicit that, without multi-viewpoint observations, all measured speeds are lower limits.","pith_inferences":["If the 800 km/s speed is confirmed, models of nanoflare heating should consider energy release rate, not just total energy: faster ejections imply a larger fraction of stored magnetic energy is converted into motion in a few seconds.","A direct test is to run MHD simulations of an untwisting flux rope and synthesize EUI images; if the synthetic time–distance maps reproduce similar 770 km/s slopes without real plasma ejections, the apparent-motion alternative becomes serious.","Another test is to search the short-exposure flare images from the EUI campaign for even shorter-lived nanojets; their absence at 0.04 s exposures would suggest the 2 s events are partly motion-blurred.","If real, these fast nanojets could power small-scale wave or shock signatures in the corona, observable as Doppler shifts or intensity disturbances in coordinated spectroscopic data."],"forward_implications":["Component reconnection can produce sub-Mm plasma ejections at speeds near the coronal Alfvén speed, so nanoflare-type energy release in dynamic coronal environments can be far faster than earlier surveys suggested.","Because the measured speeds are plane-of-sky values and the fastest event is $\\sim$800 km/s, the true speeds are at least as high as reported, and could be higher.","The short lifetimes (mostly under 10 s) imply that cadences longer than about 4 s will miss many of the fastest nanojets; 2 s cadence or faster is needed to sample the population.","The estimated kinetic energies, $10^{22}$–$10^{25}$ erg, remain in the nanoflare range even though these jets are smaller than previously studied ones, supporting the nanoflare contribution to coronal heating."],"supporting_citations":[{"why":"First report of coronal nanojets and the slingshot reconnection model; supplies the baseline speed range this paper exceeds.","marker":"Antolin et al. 2021"},{"why":"Numerical simulations showing curved-field-line reconnection ejects nanojets perpendicular to field lines; used to justify the component-reconnection interpretation.","marker":"Pagano et al. 2021"},{"why":"Early IRIS observation of small-scale jets interpreted as nanojets; establishes the prior speed and scale baseline.","marker":"Chen et al. 2017"},{"why":"Follow-up nanojet observations and energy estimates; used for comparison of sizes and speeds.","marker":"Chen et al. 2020"},{"why":"Reported nanojets in stable active-region loops with speeds below 250 km/s; comparison case for why the new environment yields higher speeds.","marker":"Patel & Pant 2022"},{"why":"Statistical study of nanojet properties; supplies the size and speed distributions this paper compares against.","marker":"Sukarmadji & Antolin 2024"},{"why":"Large-scale X-ray jets with an intermittent fast component near 800 km/s; used as context for how unusual such a speed is.","marker":"Cirtain et al. 2007"},{"why":"Coronal Alfvén speed estimates up to roughly 1000 km/s; used to argue 800 km/s is comparable to the local Alfvén speed.","marker":"Anfinogentov & Nakariakov 2019"}],"fun_headline_variants":["Nanojets in erupting filament hit record 800 km/s","Fastest nanojets yet: 800 km/s in solar eruption","Untwisting filament drives 800-km/s reconnection jets","Solar nanojets accelerate to coronal Alfvén speed","Tiny solar jets reach 800 km/s, fastest ever observed"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The claim assumes that the fast-moving bright fronts seen in the EUI images are real plasma ejections moving across the sky, not an apparent pattern caused by the filament's untwisting, projection of its three-dimensional shape, or a traveling heating wave; the paper lacks simultaneous multi-viewpoint observations to rule out those alternatives.","fun_headline_variants_meta":{"raw":{"variants":["Nanojets in erupting filament hit record 800 km/s","Fastest nanojets yet: 800 km/s in solar eruption","Untwisting filament drives 800-km/s reconnection jets","Solar nanojets accelerate to coronal Alfvén speed","Tiny solar jets reach 800 km/s, fastest ever observed"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000603,"raw_usage":{"total_tokens":2818,"prompt_tokens":955,"completion_tokens":1863,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":571,"completion_tokens_details":{"reasoning_tokens":1774}},"tokens_in":571,"tokens_out":1863,"duration_ms":14264,"temperature":1.0,"reasoning_tokens":1774,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-16T05:23:12.994241+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"A decisive test would be a coordinated observation of the same erupting filament from a second high-resolution EUV viewpoint, reconstructing the three-dimensional motion of one of the tracked fronts to check whether its true velocity is a radial ejection near 800 km/s. Failing that, a calculation of the apparent speed produced by the filament's untwisting, using the observed rotation and geometry, could show whether the time–distance slopes are compatible with pattern motion alone; if they are, the nanojet speeds would be overestimated.","supporting_citations":[],"review_version":1}