NEOfixer FAQ

NEOfixer aims to help optimize the discovery and follow-up of Near-Earth Objects (NEOs) by providing observers with targeting recommendations, specific to their site. A follow-up station might have hundreds or thousands of NEOs and NEO candidates to choose from on any given night, however the value of observing one object vs. another can vary greatly. NEOfixer attempts to elevate the highest priority objects for observation, guided exclusively by planetary defense concerns, while spreading the follow-up load across the community.  

Community follow-up capacity is finite, and some objects have time-critical observation windows which if missed, may result in a lost discovery or recovery opportunity.  On the other hand, some bright objects are over-observed, with the majority of observations contributing very little to actual orbital improvement. One of NEOfixer’s goals is to ensure that the community’s effort is strategically placed to capture high priority objects during critical periods, and to shift unnecessary observation effort to objects that will benefit but might otherwise be overlooked.

NEOfixer assigns quantitative values to five fundamental sub-scores, in order to calculate priorities for each target:

• Importance: How important is the object, from a planetary defense perspective?  This can be estimated by combining its size (using H magnitude as a proxy), how closely it can approach Earth (using the Minimum Orbital Intersection Distance, or MOID), and its impact probability.  Large NEOs with small MOIDs and elevated impact probabilities have the highest Importance; small and distant NEOs with no chance of impact have the lowest Importance.  Objects that are conclusively not NEOs (q>1.3) have zero Importance to NEOfixer.

• Confidence: How confident is NEOfixer that an object exists, and/or the observations are properly linked?  This principally affects new submissions to the NEOCP.  Confidence is determined by the discovery program’s prior history of NEOCP submissions, and may also be influenced by reports of negative detections from other observers.

• Benefit: What will be the expected improvement to an object’s orbit, if new observations are obtained?  NEOfixer estimates this by comparing the current sky-plane uncertainties to the expected astrometric accuracy of the potential new observations.  A hundredfold reduction in sky-plane uncertainty is roughly equivalent to a 100x improvement of our understanding of the orbit.  For two hypothetical objects that receive the exact same benefit from new observations, NEOfixer places a higher value on improving the more poorly known orbit (the orbit with the higher U parameter). 

• Urgency: What is the cost to image an object now, vs. some other time in the near future?  Urgency increases if the object is becoming more costly to observe (due to uncertainty, Galactic confusion, or required exposure time), or decreases if the object will be easier to observe after tonight.  Urgency will also decrease if other follow-up observers report interest or success in targeting a particular object. 

• Cost: How much telescope time is required to successfully image this object?  NEOfixer estimates the subscribing site will need to image the object three times, to SNR=5, covering the full +/- 2-sigma uncertainty region.  Estimated exposure times account for the site’s instrumentation, the target’s V magnitude, plus the sky brightness, airmass, and stellar confusion at the time and location of the target.  The number of pointings required to tile an uncertainty area is determined by the instrument’s field of view.

Final priority is estimated by multiplying Importance * Confidence * Benefit * Urgency, and dividing by Cost.  For convenience the score is then translated into a linear scale, from zero to about 10.  An object’s priority may change throughout the night as Cost, Benefit, or other values change, for example when new astrometry reduces the sky-plane uncertainties.  The priorities listed on NEOfixer’s main table correspond to each object’s maximum priority for tonight, where “tonight” is defined as the night currently in progress at a site, or the upcoming night if NEOfixer is consulted during the daytime.

Please note that while NEOfixer is developed and maintained by Catalina Sky Survey personnel and collaborators, there are no survey-specific weightings applied to any object.

A high-level summary of NEOfixer’s workflow is this: for each object, for each follow-up station, for each time in the ephemeris, calculate a unique priority score.

NEOfixer fetches astrometry of all cataloged NEOs from the Minor Planet Center (MPC) database, plus astrometry of NEO and comet candidates from the NEO Confirmation Page (NEOCP) and Potential Comet Confirmation Page (PCCP).  These are the fundamental data products that feed NEOfixer.  Supplemental information comes from the JPL Center for NEO Studies (Scout and Sentry impact probability, NHATS, Yarkovsky candidates), NEODyS (impact probability), and MPC (multiple designation assignments, historical NEOCP outcomes).  NEOfixer also incorporates feedback from follow-up stations regarding their intent to observe particular NEOs, and the outcome of those observations.

Astrometry is separated into objects, and orbits are determined by Project Pluto’s open-source orbit-fitting code Find_Orb.  Note that the orbits, ephemerides, and uncertainties determined by NEOfixer all come from Find_Orb, and are independent from other orbit computers such as MPC or JPL.

For each orbit, a geocentric ephemeris is generated (MPC code 500), running forward a few weeks into the future.  NEOfixer then checks to see which sites can potentially observe each object at some point during the look-ahead period.  The object is then scored according the criteria outlined above (Importance, Confidence, Benefit, Urgency, Cost), and is inserted into that site’s list of potential targets.  When all the objects have been scored, the list is sorted by priority and presented as a large table.  The amount of work that NEOfixer needs to do to pre-calculate all this information scales with the number of objects (cataloged NEOs and NEOCP objects), the number of participating sites, and the length and resolution of the look-ahead ephemeris (e.g. 3 weeks of ephemerides, every 15 minutes).

NEOfixer maintains a rapid refresh cadence, so when new astrometry is published by the MPC, or information about an object is updated from an external source, NEOfixer detects the change, reprocesses the orbit and ephemeris, re-calculates the score for each site, and publishes the new information.  Objects are updated typically within a few minutes of new information becoming available.

The NEO follow-up community is large and diverse: participants range from full-time funded NEO programs operating multiple telescopes, to occasional users of shared-use telescopes, to unfunded but highly capable small-aperture stations.  NEOfixer is designed to serve the community’s full range of capabilities, and also to work with varying levels of interaction from observers.  Some follow-up stations may choose to tightly couple their nighttime operations with NEOfixer, others may prefer to build their own target lists, and still others may not interact directly with NEOfixer at all.  NEOfixer can benefit, to varying degrees, from all of these types of observers.

• Tight coupling to NEOfixer: Stations following this model will consult NEOfixer for target recommendations, and will promptly communicate targeting intentions and outcomes, probably using the NEOfixer API.  This will be done throughout the night in a continuous communication loop.  Given NEOfixer’s dynamic scoring, this observer may populate a queue at the start of the night based on NEOfixer’s recommendations, but will update that queue frequently, consulting NEOfixer to see if priorities of upcoming objects have changed, or whether new high-priority objects are available.

• Loose coupling to NEOfixer: Some follow-up stations may be scheduled in batch mode, with limited ability to modify a queue once the observations are scheduled.  Other stations may have their own criteria for building a nightly target list, different from NEOfixer’s.  Both of these stations can usefully communicate to NEOfixer their targeting intentions, via the website or the API, regardless of whether NEOfixer was consulted in scheduling the objects.  This will help NEOfixer adjust object priorities for the rest of the community, potentially helping to avoid duplicate observations.

• No direct interaction with NEOfixer: Some stations may not directly interact with NEOfixer, but when their NEO observations are published by the MPC, NEOfixer will automatically re-calculate the orbit and adjust those objects’ priorities.  Low-latency reporting and publication of astrometry will ensure these observations have the greatest impact.

The more follow-up stations that communicate targeting intentions and outcomes to NEOfixer, and that request targets from NEOfixer, the more effectively the community will build and improve the NEO catalog for planetary defense.

When follow-up observers communicate their targeting intentions and progress toward completed observations, NEOfixer can use this information to help adjust objects’ priorities for other stations.  For example, if three stations plan to observe an object tonight, then there is a good chance of getting at least one set of successful observations; therefore the priority shown to other stations (where the object is not scheduled) will be lowered.  The cumulative communications from all sites about a particular target can be thought of as the “interest level” for an object, with higher interest serving to decrease priority.

Observers can communicate several actions about an object, each holding a different weight: May Observe, Will Observe, Observing, Observed, Found, Not Found, Reported, Cancelled. In the case of successful observations, these self-reported actions are superseded when new astrometry is picked up by NEOfixer, after being reported by the observer to MPC and published.

Some observers may be hesitant to share their targeting intentions, as they may be unsure if the observations will be attempted, let alone be successful, and do not want to discourage other observers from also targeting the object.  Please know that NEOfixer attempts to weight each communication appropriately, so that the announcement that a high-priority object has been scheduled at one site will not revise the priority drastically downward for other sites.  A site’s previous history and reputation is also considered: if a site that typically observes NEOs brighter than 20th magnitude suddenly claims they will observe a 23rd magnitude NEO, then NEOfixer will assign very little (probably zero) weight to such a claim, and the priority will remain unchanged.  However, if there is a sufficient level of interest around an object, then NEOfixer will decrease the target’s priority, implicitly suggesting that other observers concentrate on other, higher priority objects.

NEOfixer is designed for use by active NEO follow-up stations.  The minimum requirement to get started is access to a telescope with an MPC code.

Navigate to the Register tab, and request an account by providing your name and contact information.  After an initial approval, you can A) create a new configuration based on your MPC code (if you are the sole operator of this station), and/or B) add an existing telescope to your profile (if you are authorized to use a previously configured station).  Your profile can contain as many telescopes as you are authorized to use.

Configuring a new telescope within NEOfixer requires information about the site, telescope, instrument, and limits.  This information will allow NEOfixer to determine which objects are observable from your site, and to make customized priority scores, based on the capability of your instrumentation.  Approving a new telescope and calculating scores for all possible targets may take up to a day, so plan to allow enough time before expecting to use NEOfixer at the telescope.  However, after the initial setup process, every registered site will be kept up to date.

The Targets table lists all objects that NEOfixer determined to be potentially observable from a particular site.  There may be hundreds or thousands of targets that are visible, depending on a telescope’s capabilities.  Note that most columns can be hidden or made visible (see the “Column visibility” drop-down menu), and re-arranged by dragging and dropping.  The Table can be sorted by the values in any column: click the column heading to sort in either increasing or decreasing order.

In order to create an actionable target list, users may choose to filter the table entries.  Click the “Filters” accordion tab, and set Min/Max values as desired.  Search for any object by designation (packed or unpacked, numbered or provisional) using the “Search” box near the upper right.

The targets table updates frequently as new information becomes known about objects, so you may note the ordering of objects and their assigned priorities changing throughout the night.  It is recommended to double-check an object’s priority before beginning to observe it from your site, in case it was recently observed by another site, potentially reducing the priority for more observations.

The “Action” column can be used to communicate targeting information from your telescope to NEOfixer.  This can also be done programmatically via the API.

Click on any designation in the target table, and a new page will open with more information about the object. There are several tabs:

• The NEOfixer Plot at the top shows the NEOfixer priority score and other sub-scores as a function of time, beginning tonight and running for several days. This plot is interactive and can be panned and zoomed.  

• Orbital elements and uncertainties, as written by Find_Orb

• A topocentric ephemeris, displaying time, position, rates and magnitude, as well as other site-specific quantities such as predicted exposure time, estimated sky brightness, Galactic confusion, and 1-sigma positional uncertainties.

• A plot showing the benefit that each tracklet provides to the calculation of the NEO's orbit.  The reporting latency of each tracklet is also plotted, along with the evolution of the orbit's U parameter.  Tracklets are sorted by time of reporting to the MPC.

• A listing of the astrometric observations used to calculate the orbit

• Residuals of each observation (from Find_Orb), along with a list of contributing MPC codes

• An interactive orbit viewer which plots the object’s nominal orbit in the solar system

All these tabs except for the orbit viewer have API links at the bottom of each section.

Yes. Users can query NEOfixer to get astrometry, orbits, ephemerides, and priority information in either plain text or JSON format. Targeting status can also be sent to NEOfixer via an API. Refer to the API instructions.

No. NEOfixer recommends targets, but does not provide queue management or telescope control services. Individual follow-up sites are best positioned to operate their telescopes and to collect, reduce and report their data. NEOfixer does provide topocentric ephemerides from Find_Orb, complete with estimated exposure times, positional uncertainties, and rise and set times, which some observers may find useful in scheduling their telescopes.

Observers can customize NEOfixer’s recommendations by applying filters on magnitude, uncertainty, rate, sky position, source (NEOCP vs. catalog), etc. This may be useful if, for example, it is difficult to schedule objects that require multiple pointings, or if the local sky conditions are less than ideal, or if available telescope time is limited to part of the night.

NEOfixer will likely promote some challenging targets at elevated priority. Remember, the estimated cost in telescope time is included in NEOfixer’s calculus, so if a very faint or highly uncertain object is assigned elevated priority, this means that NEOfixer deems it worth the cost of those expensive observations, based on higher values for one or more of the other scoring factors (Importance, Benefit, Urgency). However, if you find that NEOfixer consistently promotes objects that are impossible for your site to observe, then please contact us to discuss tuning NEOfixer’s telescope configuration for your site.

Remember, NEOfixer evaluates each object from a planetary defense perspective. There are many objects in the NEO population or posted to the NEOCP/PCCP which may be interesting for reasons not directly related to planetary defense (comets, mission-accessible objects, interstellar objects, NEOs with interesting physical properties). These objects will be ranked based on the scoring criteria outlined above, which is strictly focused toward planetary defense interests.

Quantifying the value of a set of NEO observations is necessarily subjective, but NEOfixer provides a framework within which to explore this idea. NEOfixer estimates the value of obtaining new observations of any NEO, from any site, for all time (in the near future). That same calculus can be turned around to examine what was the actual benefit, now that the observations are in hand. We can start by taking the discovery tracklet of any NEO and progressively fit orbits, adding one tracklet at a time, while estimating the sky-plane uncertainty at the time and place of the next tracklet. This gives a proxy measurement for each tracklet’s Benefit to the orbit, which can be weighted by the object’s Importance to planetary defense.  NEOfixer provides Benefit Plots under each object page, which illustrate this method of estimating the benefit of historical NEO observations.

One advantage of this technique is that it can be done for any object, provided the time of submission to the MPC is known (observations that languished for hours or days between observation and submission may end up providing little to no benefit to an orbit, if observations taken later were incorporated sooner).

By tallying the value of all observations, and dividing them into useful categories (e.g. all observations by a given MPC code, or within a certain time period, or from NEOfixer users before and after adopting NEOfixer), we can measure whether the community is spending its observing time efficiently, and identify specific sites or classes of objects representing potential areas for improvement.

Feedback about NEOfixer is very welcome. Please use the Contact form.